Headers, headers, headers... Single most beneficial mod which you seem to ignore. Up your budget, get headers and 1.9's and call it a day. You'll have to shell out a few $ to have the overkill tune reworked, but it'll pay off. Plog is just 1/2 a header install... Never made sense to me at all.
Non-realistic expectations vs underfunded reality. And modding doesn't invite reliability issues unless you buy cheap crap and do a butcher job.
Cheap/Fast/Reliable
you CAN have two of the three... Chose wisely.
if you're looking a small blip of difference and have only a smidgen to spend, save it, you're better off, because what you've posted that you'd do, will make little difference in your drive. My current DD I've put thousands into it, from suspension, to audio and its a BIG difference. Funny thing is (knock on wood) I've had ZERO failures, broken parts, etc. You can check my link to see what I've done and it all works wonderfully without a hitch. Well, the 255 tires was a mistake, lmao, but I've since gotten over it.
Anyways, as a suggestion I would say you need to do a little more research and base your expectations on reality so as to not set your self up for a big let down when you spend your $500 and don't notice much difference. You gotta pay to play! No way around it. Lol