2004 Ford Mustang 3.8 V6 Convertible, best advice for minor performance increase?

You'd need more than a simple chip etc., to make your Mustang faster than a modern V6 Camry or Accord. Those cars make 70+ more horsepower than your Mustang and a convertible Mustang isn't lighter than those sedans either.

You could probably install a basic nitrous oxide system for ~$700 if you do all the work yourself. Several companies sell ready-to-install dry nitrous kits (some specifically for Mustangs...) that can increase peak power by at least 75hp at (but only at) wide open throttle on an otherwise stock motor without creating major reliability issues. That's probably the cheapest (and only) way to achieve your performance goal without spending well into the $1000s on modifications.

If it were me though, I'd just accept that the car you have isn't a fast car and live with the car the way it is. Every nice sunny day, put the top down and enjoy the sun and wind in your hair knowing that the guy in the V6 Camry or Accord can't do it but might wish he could.

The thing is that even New Edge GT's have a tough time with the newer V6 Accords and Camrys. There's nothing you can do short of forced induction that will enable you to accomplish your stated goals.

Unfortunately, modifying engines is not cheap in general. The simple fix is something like a super charger but it probably costs you about 4k. The old mustang V6s are prehistoric and it's kind of hard to cheaply modify them

So you say your family is not well off and then you don't want to help them you want to be able to beat the family car, do you know how that makes you look?

if you are not well off then you should not be trying to do something that is going to cost a small fortune to do.

Cause there is NOTHING you can do to a 3.8L for cheap and get any actual noticeable amount of HP from