Can anyone suggest a nice place with reasonable prices in Santa Monica at the end of July?

You might check out the prices at the Radisson Huntley in Santa Monica or, alternatively, the Best Western Marina Pacific, which is actually in Venice, but close to S.M.

I stayed at the Best Western Santa Monica Oceanfront about 2 years ago for $79 and thought it was great. It is directly across from the beach and very short walk to the pier and the Third Street Promenade with all the restaurants and shopping. It was very clean and seemed new at the time. I would stay there again in a second.

travelingirl is giving you a great suggestion-- Surfergirl's suggestion of the BW Marina Pacific is very good too. Both are clean properties in good locations to see interesting things.

Also in the area: A Holiday Inn on Colorado at Ocean (a half-block off the SM Pier), and a Four Points Sheraton on Pico at Fourth. These come up in Priceline bids.

I assume you've noticed that hotel rates in the SM area are pretty high. You may want to attempt Priceline (look on biddingfortravel.com for hints on bidding in this area).

Try the Ambrose Hotel..it's brand new, though it's 20 blocks from the water.
http://www.ambrosehotel.com

The Ambrose looks quite nice, but it's smack in the middle of nowhere you want to be in Santa Monica, unless you're visiting someone at St. John's Hospital or buying a car (most of the SM car dealerships are around the corner on Santa Monica). Better to stay closer to the pier and save the driving for the rest of the LA area.