Hotel Banys Orientals has been on top ten of the Conde Nast list for best hotels in the Med area, it's in the great El Born district and it's only 105€/$135 pr. night.
http://www.hotelbanysorientals.com/

With 6 nights, I would find a flat to rent. There are numerous places aroun Placa Catalunya and you will save by being able to make your own breakfast. Plus you get to pretend you live there..

Hi Kimhe, I have read (and reread) your Cataluña Trip Report and loved it. Thanks a lot for the rec, the hotel looks wonderful and the price is extremely reasonable!

uhoh_busted, even when we have rented flats we have found ourselves going out for breakfast as I have never mastered the barista art and I love a good, frothy Spanish coffee. Now, the prentending part I do love...

I would rent an apartment for those nights.
This time I found one through Booking.com in Placa Catalunya area (more central) as we are flying to Denver and we only have a couple of days to sightseeing.

In 2010 we stayed in Barceloneta area for a week. I would avoid it if you like to sleep at night. Too much partying and very loud at night.

Plenty of coffee and breakfast places around Hotel Banys Orientals, but I would recommend tiny Mesón del Café dating from 1909. 150 meters from the hotel and great atmosphere, although breakfast places all around Spain are often very atmospheric, making this the ideal start of the day and ten times better than any boring hotel breakfast.
Mesón del Café: http://www.coffeebarcelona.com/en/barcelona/34-coffee-establishments/55-meson-del-cafe

I'll second Hotel Banys Orientals. We stayed their in April at a rate of 105 euros/night plus 8% tax (unusual for Europe that the tax wasn't included in the rate). The hotel has little extras like all the bottled water you want in a fridge on each floor. Our room was big by European standards. Best of all is the location on a nice mostly pedestrian little street with nice bars, restaurants and cares around, and very convenient to the metro and most attractions. I was apprehensive about staying there, but would love to go back,

If you want to be on Gran Via just five minutes walk to the Placa Catalunya, we liked The Hotel Gran Via which will probably be under your announced budget. It is in old colonial style with a dramatic staircase, large rooms and bathrooms. Ask for a rear room for complete quiet. It is the first picture in this group of scanned Barcelona pics.
Passeig Gracia with it's Gaudi buildings starts a block from the hotel and the hop-on, hop-off turistica busses tsart at the Placa. Plenty of breakfast choices in the area...we liked the kiosks at the famous Boqueria, just a little way from the Placa. (Hotel has breakfast also)

https://picasaweb.google.com/stuarttower/SelectedBarcelonaScenes#

mari...Gran Via website:

http://www.hotelgranvia.com/

thanks stu! This is also a great recommendation.

Loved Regencia Colon, location could not be better.

All the hotels mentioned above are too expensive (for me).... I'm sure Banys Orientals is nice .. Wow nice looking on the photos.

My budget and modest accomodations : 1) Pelayo Hotel - Guest House was €28.- single room (was small of course but not tiny), but with a large (almost as large as the room itself) bathroom. That was in early December 2011. Considering the price, it was quite ok. Only 2 minutes walk from Plaça Catalunya toward the University. Breakfast not included.
http://www.hotelpelayo.com/?idioma=en

2) Hostal Centric : €45.- a room with a big bed (for 1 or 2 persons) January 2012. On Carrer Casanova, 5 minutes walk from Plaça Calalunya. Also breakfast is not included. I returned here because 1 year ago, I paid even less €40 and got a room with a large bathroom with tub. This time the room was smaller and with only shower but it was perfectly fine.
http://www.hostalcentric.com/i_htm/i_index.asp

I didn't have noise problem or any other particular problem at either accomodation. If OP is really budget minded (still want a descent quality ) then it would be worth check these two. 15 - 20 years ago I stayed at other cheap "hostals" but compared to them, these 2 are muc better. Both had air-condition so can be a good option in summer as well.

For a 6 night stay i would recommend enjoybarcelona.com and book an apartment instead of a hotel!

An apartment stay has always been ideal for me as i can cook my own breakfasts (i tend to like a big breakfast rather than just a pastry and coffee as is most commonly available from the local cafes in the morning), and after walking around a heap during the days it is better to relax in comfort in your own lounge room rather than in a hotel suite with just a bed and an ensuite. It makes you feel like a local and is better value than a hotel. You can find plenty of apartments on their website within your price range and it is easy to get the keys and settle in.

El Born will let you stay right in the middle of it or Gracia is also a good choice as you are in a bohemian artists' village in the middle of the city! Gracia is a slightly longer walk to anywhere whereas Born is in the think of it (the area links Barceloneta with the Gothic Quarter) but in summer can feel very touristy and some apartments can hear a bit of noise. For me, the Gothic Quarter and Raval are great to walk around but too dense and loud at night for me to want to set up sticks there. At night from a Gracia apartment, the noise level is low while the street life is vibrant within walking distance to some great cheap eateries.

We stayed at Hotel Constanza. Nice hotel and good location for exploring central Barcelona.
http://www.hotelconstanza.com/

We like th Hesperia chain and are in reat locations.

Thanks to all for the great recs.

Kappa, those are not bad at all!!

sorry Kimhe, I just realized I confused you for a second with Kwoo. But I have also read a lot of your wonderful suggestions!

Kappa opened up a world of possibilities! I had not even considered options in that price range.

Has anyone had any experience with Hostal Q? Its very close to Plaça Catalunya. It seems modern, clean and certainly a great bargain at 80Euros the night. Gets great reviews in TA.