You can get a wheelset with cog and lockring for $100 (look at bikeisland.com). I'd budget $25 for a bottom bracket (you'll want a 103mm bottom bracket to make a nice chainline with your new track wheels, consider the Tange at benscycle.net), another $50 for a cheap crankset (look for Origin 8 on eBay) and $10 for a chain.

You'll probably also want new brake cables and pads ($20-$40 total). You'd do well to overhaul the headset, which means about $5 for ball bearings. New tires and tubes are also likely in order. If you're going to ride it much, you should plan at least $50 for this. If you need new bar tape, figure on $10 for that. You can get really nice brake levers for $20. Figure $10 for grease.

Finally, there's the question of whether or not you have or can borrow all the tools you need. If you have the tools, you're looking at about $350 to do the project right. (Not coincidentally, this is the price of the cheapest brand new fixed gear bike on the market.)

Anyway, I don't mean to scare you away. For the above investment you'll also get a lot of first-hand knowledge and a deep bond with your bike.

The question about the bottom bracket has to do with how it's threaded. I'm not sure if that was clear from the previous discussion. Most new bottom brackets use what's called English or ISO threading (1.37" x 24 tpi), some older Raleigh's used a Raleigh-specific threading (1 3/8" x 26 tpi) which isn't compatible. The thing to do is hope that you don't have that. Your LBS can probably help you figure it out.