Having just received your C&R, you might want to check this site over;
www.surplusrifle.com. Read a few posts on the Mosin forum and you should be able locate where to get a Mosin. You should also be able to get a line on the best ammo currently available.
The real cheap ammo is usually corrosive. That's not a big deal as long as you properly clean your rifle after shooting.
At Surplus Rifle, locate the Home page. Look at the upper left column and click on "WWW Links". There should be a list of C&R dealers there.
Prepare to begin spending money. C&R's can be addicting and Mosins are a good bargain. There are many out there that have been arsenal refinished and are in excellent condition. It should not be hard to find a very nice 91/30 or 44 for far less than $100. Model 38's tend to be a little more, but are still a bargain for what you get.
Good luck and have fun.