well if you only want a slight drop, nothing more than 1.3 inches, then I would get the FMS c springs from www.gefracing.com, summit will price match adn may offer free shipping so check with them, they run 120~ or so and the rate is 650/350 very nice rate and drop and you wont need cc plates to maintain the near stock alignment specs (they are a good idea however but can be put off for a bit)
next with the extra 250 i would get mach 1 tokicos (shocks/struts) that will leave you just a little bit... go to a junk yard and get a rear sway bar from a 99+ gt and maybe a set of maximum motorsport endlinks for the front sway bar.
after you save up some more get maximum motorsports lower control arms NO OTHER BRAND lol these are just designed better so get them.
after that go with some chassis bracing, full length subframes (good any time... very nice items)
thats up to you, I however would take the rims due to it changes the looks of the car TOTALY and those floppy 15s look horrid.... you can get a set of 17 by 9 03 cobras for 600 bucks to your door just needing 275/40/17 tires NO OTHER SIZE!
I'm not sure what all you can do for $400 aside from something like the bullitt kit or the mach I kit. They are around that price and include c-springs with shocks and struts, Mach I may come with swaybars, I'd have to look. $400 isn't much!