I haven't built a small scale model in years but this sounds like fun so let me ask a couple of questions to see if I fall within your "rules".
I bought a 1/25th "Revell Muscle" '71 Plymouth Hemi Cuda a few years back (as reference) for a 1/8th scale Cuda I'm working on, I was somewhat disappointed as the kit has no shocks , clunky inner wheel halves, wrong interior pattern and to top it all off just doesn't just doesn't look right.
I bought it a Hobby Lobby with a 40% off coupon so the kit cost me about 12 bucks. I also have a resin Gibson Super Stock engine. The engine was given to me by a friend but they cost around twenty bucks or so depending on where you buy them.
I have plenty of paint on hand from other builds including tubes of acrylics (used to be an artist) that occasionally I dip a brush into for weathering etc.
Like I said....I don't normally build small scale so I have no large stash of parts. The only kit bashed parts will be disc brake calipers taken from a broken die cast model.
You all are familiar with the Plymouth "Super Bird" I'm sure, what I have in mind is turning the Cuda into "Super Fish" as if Plymouth had built it as a street muscle car in the '70's to complete with the Judge, Boss etc, cars of the era. I have no way of figuring scratch built parts as I generally use scrap plastic, house hold throw aways and I buy fillers, sand paper etc, in bulk for full size stuff.
So it's up to you guys... do I qualify?
How about list it as say...$30 for both the model and the motor. That way you have some plenty of room to add paint. Sound fair?
About paint also, what If I can prove the spray can was cheaper than the $3 general cost?
I think to keep it even, I'd have to say count it as $3.
I totally agree with you, the JPS is one of my all time favorites behind the Day Glow Orange Mclarens. Just gives me goosebumps In fact I have already decided to eventually pick up another one of these kits and make the JPS 98T
Edit: That's interesting. I didn't know that about the Camel decals. I guess my kit must have been an older version because mine also had both sets.