I'm looking for some help 1966 Barracuda

Matching numbers? Nothing before 1968 had matching numbers. Overused phrase, much like "rare" which these cars certainly weren't.

The parts you need are available from time to time. Keep an eye out on eBay, various Mopar oriented forums, and Mopar specific junk yards. You'll be looking for used parts, as not much is reproduced for these cars.

What should you spend? What is it worth to you? An original Formula S in showroom condition might be worth $10,000, but it would cost far more than that to restore a "restorable" car. Keep in mind this is a 45 year old economy car. A-bodies are a lot of fun because they are inexpensive. $5000 for a complete rust free early Barracuda is probably about the top of the average.