there are lots and lots of turbos for that engine. check the turbo section of this site for some. Many popular choices are mitsu turbos like the 20g and 16g, hybrids of them like the t03/t04e, and another is the the t60-1. These are just a few. You can find almost an unlimited amount. This is because the reason a turbo fits is because of the turbo manifold, not the engine itself. If you can find or have made a manifold that matches your block and the turbo you want, your in business.
for the b18b stock, your looking at pretty low boost levels - but still a considerable gain. The boost you can run all depends on what turbo you use. Bigger/smaller turbos act differently at different PSI levels due to CFMs, read up in the turbo section of this site for more on that.
A nice, brand new turbo will run you for about 500-600 dollars, but I don't know alot of people who pay that. Most will buy their turbos used from friends, or get them from a junkyard. But if you want a new one - thats what a nice one usually costs.
You can run on a stock setup with low boost, and finally, I would reccomend getting an intercooler. It allows you to run more boost in the future, and for now, it helps keep the heat levels down - which is always good
hope this helped