I'd build my own. For a fraction of the cost of a crate motor, get the machine work done, buy your own parts.
I just had my engine for my race car done. Machine work, cam bearings, and pistons pressed on rods was around $350 CDN. The pistons were $180 for .030 flat tops with the 2 valve reliefs. Plus bearings are cheap, so really if your on a tight budget building your own would be a good way to go. Assuning you have the urge to learn to build a engine.
I guess if money isn't so tight a crate engine would be the way to go, with a warranty etc. I'm going to have my engine ready to go for under $800. I did already have a 350, and a steel crank so that would have added some money.