http://coilspring.com/
- Renton Coil Spring (where I work)
They specialize in high performance materials and applications, titanium and steel for aerospace, nascar, nhra etc. I doubt you would be able to get anything sub 500$ though as it is a job/specialty shop :/
Seems like a garage door spring or something similar could get you in the right ballpark but for that much force and acceleration the systems would be come quite scary and heavy!
Find one of those playground toy springs
You could look into gas springs, but I think generally they will be slower than you are looking for. Maybe with a lever or other way of adjusting speed/force.