is it possible to buy just a 10/22 action.... ?

Yes you can. Heres one, I'm sure if you shop around you can find it cheaper.
http://www.stockysstocks.com/servlet/the-143/Power-Custom-10-dsh-22-Grand/Detail

if you are talking about the receiver you can find them VQ makes one as do a couple others but normally it is as much as you can find a good used one or even buy a complete rifle and sell all the extras. the last 2 I bought new when they were on sale for $150 sell the stock and barrel and you are only into the complete receiver bolt and trigger around 100. I have also bought a couple at pawn shops for not much more than a 100 and then sell the parts you do not need.

Try Shooters Discount, Factory Ruger recievers,trigger groups,bolts etc. Use them several times and highly recommend

Do a search!

I don't remember where I found it, but.....

I found a detailed site a while back, where a guy made a 10/22 receiver out of a piece of square tubing, and built an M1 carbine replica.