A hard cast 240 grain bullet would do just fine. That is what I use in mine. I have tried the 300's but found them to be just a little bit too long for my 1894's. But I have a couple of friends who shoot the 300's with no trouble.
I am not sure where you are shopping but excellent condition used ones can be found with some regularity for prices between $400-$550. I have bought and sold three in the last year. I can pick them up here in WV for around $400 most of the time. then I resell them on the net for a $50-$100 profit. Tom.