Check Ebay. Bayonets usually go for around 30-40 bucks these days. SAVE MORE SURPLUS has couple of bayonets for sale, but their prices are a bit too high.
All Eastern Block made bayonets are pretty much the same, except for trades and colors. Any modern models made for AK74 will fit SLR.
If you really want to get Russian bayonet, get this:
This page has all the info you need to know about AK bayonets.
http://tantal.kalashnikov.guns.ru/bayoindex.html