A similar question was addressed, but not thoroughly.

I would like to know what relatively inexpensive upgrades and
modifications can be made to a "regular" car (in my case, a '95 Ford
Taurus) to improve performance, fuel economy, and most importantly,
power.

Inexpensive would be under $250; the cheaper the better. A car that
old is not worth dumping too much money into. Examples would include a
performance module (I made one for ~$30 that tricks my IAT sensor into
holding a constant temp, estimated average gains of 10-20 HP across
all makes/models), an electric supercharger ($90-$300 depending on
make/model providing estimated increase of 15-40 HP), etc.

I've heard something about a fixed intake fan called the "turbonator"
or "spiralmax;" I think the product is a scam, but I'm interested in
finding out if something like this could be a viable option.
Additionally, spiralmax.com advertises a Turbo Exhaust Tube which is
supposed to create a vacuum in the exhaust, letting the air out faster
for better performance. Is this also possible?

For clarification, my car has no warranty issues. Any modifications
that involve altering the engine (boring out holes, replacing pulleys,
etc.) in some way are welcome as long as they fit in the price range.
If a part fits the price, but the cost of fitting that part onto the
vehicle exceeds $250, I'm not interested.

well if you are looking for fuel economy and power then i would sugest
alowing your car to breath better buy replacing your air filter with a
high flow air filter or maybe a cold air intake (check ebay) and a
free-er flowing exhaust muffler, but with the muffler there would be
an increase in noise.  it also matters were you live, if you have to
pass some sort of emissions testing like in California. so check for
C.A.R.B. certifaction on certain products. now if you are looking for
the most hp gain for the $ it is great because it is only used when
you want it and it is not always functioning like a turbo or
supercharger would, but it will not help you with gas milage just
strait line performance, and that is nitrous oxide. now your v6 taures
will take about 20hp per cylinder so you could  run a 50 shot of n20
no problem with no other mods. and a cheap nitrous system would be NX
main stream system which reatils for like $350 again check ebay and
dont buy a used ssytem

Definately an air system, this frees up alot of unused gas mileage and
lets you feel horsepower.  Air in general is a good route here, try a
throttle body or a chip too.  Here is a good site for some ideas,
http://www.carperform.com/cgi-bin/index.pl?=&=G6H1Are