Thomas,
It's unclear whether the $1500 is for a rebuild or performance parts after a rebuild. If its the total, and you need a rebuild, then you will be lucky to
have anything left for an exhuast system even after skimping on the quality of the rebuild.

If you do need a rebuild, my advice is to get a B20, and base the rebuild and any performance improvements on that. You will end up better off in the long run as the B20 has more potential, parts are easier to get, etc.
The head is the key to significant performance improvements. You could pay me or someone else to improve a B18 head, and a lot of what you would be paying for would be just to bring it up to the specs of a stock b20 head. The B18 has smaller
intake valves, larger valve stems, valve seals that are not as affective. I can't use the parts that I normally stock, so it takes longer and costs more.

But if you have to stay with the B18, make sure its in good shape first. Do a leakdown test. Make sure the distributor is good. Have just a little work done on the exhaust port by someone who knows how to do it. Not sure which head you have, but run a 9.5 or 10 - 1 CR. Put in a performancce cam with lifters and new timing gear. Be careful of your cam choice, as most cams available were designed for B20s and could be too much for the B18, causing a loss of low end power. The stock D or K cams might be good low price alternative. A free flowing exhaust of larger diameter than stock. And leave some money to do some tuning - on a dyno.

John
V-performance.com