What would you pay for hp? ex. a K&N typhoon now averages 250-300 and will probably only give you a gain of 5-6 hp. thats about $50.00 a hp. things like that. how high are you willing to go $/hp in your search for more power and speed?

For me it's not so much a limit on how much I'd spend, it's more about bang for your buck.

example:
$350 for a CAI or $200 for a SRI and a couple less hp's. SRI wins.
$600 for 4 tires or $1000. I'll take the $600 ones.
$540 for exhaust or $490 for the same type of exhaust just different manufacturer. I'll take the $490.
$400 for headers, sounds good to me.
$500 for a ecu tune that needs to be done again every time you add a mod or $500 for a tuneable on the fly piggy back. I'll take the piggy back.
EVO spolier, just for the look or the GTS spoiler I already have. GTS wins.
$640 for some nice ASA rims or $1000 for something else. $640 wins.
Turbo for $4200, idk, I thought about it, but you can probably have one built or build one yourself for less.

etc....
bang for the buck.... if you can spend $1000 and get the same hp and torque gains that someone else got for spending $1500, why wouldn't you.

I ask because I am considering an ecu mod for my audi and its 680 + shipping for 20+ hp and 13+ tq... thats about $35 per hp but its still about $700 which is alot of money for 1 mod.... Trying to figure out if its worth the money

That's not bad for a ECU mod. Typical. I'd pay it, of course I like a piggy back better. $40-50 dollars a horse isn't bad, $35 is good. My exhaust cost $500 and prob gets me 5 hp's, that's 100/hp. So depends on the mod.
Is this a ecu flash or a piggy back?

well these freakin euro systems are so complicated... its the desolder of the chip and installation of a totally new chip so i will have to ship out my ecu overnight get it done and have it sent back.