I have been contacted by an individual interested in using my spray photos for an ad campaign.

I'm amateur, I know nothing about this.  I don't know if I even want to get into the whole sales thing.  IP rights, control of my work, etc.  Not to mention that I strongly feel that (as far as the spray images are concerned) that the helo outfit ought to have a say.

School me!

They will need releases from all the identifiable people in the photos. The normal assumption is that the photographer got those signed at the time of the photos. Sounds like that was not the case.

As for pricing, this is usually based on a combination of
- size of the photo to be used
- how the photo will be used (print, website, etc)
- the expected number of eyes that will see it
- length of the licensing term (one ad campaign, one year, forever)
- exclusive vs non-exclusive licensing
- licensing vs ownership transfer

Yup, the guys already got it nailed.  The more rights, prints, etc, they want, the higher the $$$ figure.  Just a generic image off Getty starts around $4-600 for an unlimited license with the max resolution file.  Mind you, that's a completely open license.  Rights Managed easily gets up to 10x if not more in price as it's very specific on what you can and can't do with it.

Research is good.  Not to mention either getting in with Getty as a contributor so they handle the legal work, or finding a good IP/Copyright lawyer for contracting.