rsx, celica, and many other cars built after 2000 fall just under 10k...you won't have a lot of money for mods, but they are great cars all around even stock.
A 240sx with bolt-ons won't be fast, it either needs an engine swap, turbo the stock engine or a lot of money into high compression/cams/header/intake/DIY itb setup/etc...plus the stock suspension isn't that great and there are less than 500 1998 manuals...so you are more likely to find a celica all-trac since they made like 2000 and all were manual. With bolt-ons on a 240 you can expect like ~170rwhp, which is enough to hit mid 14s...not really that great if you ask me for how much money you are going to be throwing at the car. Plus a 98 manual 240 is usually like 9-13k so you could buy the car and that's about it...no money for mods...