the Mosin is a great one to start with in my opinion (somewhat bias as I started on a 91/30) but its cheap for the rifle and ammo, even non corrosive, easy to take down which helps you get to know the process and parts of cleaning and assembly, its effective to take down any N.American game if you want to hunt, and once you run out of ammo you've got an 18 inch bayonet to mess around with. Also, its just a ton of fun.
There are even a couple on the EE now for $130, cant get much cheaper then that these days.