You're gonna be hard pressed to find a diamond bit for a good low price. However, I've heard that some hardware stores sell carbide bits for like 3 bucks a piece. You could get a lot of carbide bits for for the price of one diamond bit. Just a thought.
When I was shopping around for my Hudy lathe, I found that most places sold them for about the same price. +/- a few bucks. I ordered my lathe and diamond bit from Hudy's E-Shop. Pretty quick service. Don't forget to order the arbor.