Motorsport B303 or E303 roller cam....under $200....big bang for the buck.....Stay away from the F303...it's a supercharger cam and not ground for normally aspired engines. Edelbrock Performer RPM or Weiand Stealth manifold...decent low end and strong all the way to 7000RPM...under $200...( check for hood clearance depending on what air cleaner you have.....mine was tight...).. Edelbrock 1407 750CFM carb...Simple and effective...$220 or $175 factory rebuilt on Ebay. Motorcraft windage tray....about $60 and good for around 15-20 hp..
That's about $650...You can find GT40 heads on Ebay for around $500-$550 or buy a new set of Roush 180 or 200 heads for around $800....all in all not too far from what you're wanting to spend, but an awful lot of horsepower gain.
Regards,
Bill
PS...That's a good deal on GT40 heads from Hawaii Racing!