It will take several days to try 3 or 4 per night. It's about 16 euros each time. There are so many choices, your prices seem high for one sitting>>

whose prices, TD? [this is you, i trust?] my €50 for 2, or the guides' prices for a tapas tour?

i suspect the latter. by the time you've added in a drink at each place, and possibly coffee, i think that my €25/head compares pretty well with your €16. What's your favourite tapas so far?

This is from a SIL who traveled solo But has been to Spain many times but wanted to discover new places in Madrid

I went on two different tours. One was by a guy who also took Andrew Zimmerman around (of Bizarre Food) The other was thru Viator. Both were good and totally different: The viator one was wild and crazy and fun. The Bizarre food guy was quieter, more thoughtful, more sitting in dark plazas. I absolutely could not tell you anywhere I went. In both of them there was so much walking, talking, and eating on little windy streets. Costs? About $75 ( a few years ago). I see a lot of new groups and they all look pretty good.
I think this was the one I booked thru Viator but you can book it direct:
http://www.madridtapastrail.com/madridtapastour

I can't find the name of the other one. The are fun because you are with a bunch of other people