To Answer Your Question

Yes, JoHan made Javelin kits and promos 1968 to the end of Javelin production, what, 74 or 75?

All are fairly rare today. JoHan made the 71 and up kits (might have been a '74?) up through the '80s. Those are the most common today and the cheapest, though one will still run you $30 or more. If you get one of these, though, it will give you a lot of parts you need for a '70 project, such as the chassis, engine, glass, and a usable interior (though of course it probably won't be 100% ACCURATE for a '70).

Now on to your '70 project. I've been watching Javelins on eBay for about a year now so I have some ideas of what's going on. '70 kits are extremely rare and promos almost as rare. You can expect to pay well over $100 on eBay for an unbuilt kit, and probably that or even more for a good promo. Promo pricing seems to depend, among other things such as condition, on color.

'69s are just about as rare. I've been chasing a '69 promo for a while and they always slip out of my price range.

But '68s, they're not too bad. Unbuilt kits will still run you a good C-note or more BUT there are quite a few promos around and they go for various prices depending on condition. I've bought several in the last year in less than perfect condition in the $40 price range, some even in the $30 range. So you get a '68 promo, preferably one with bad, broken, or missing chrome to start. Modelhaus sells '70 Javelin front and rear bumpers/grilles, and taillights in resin repro. They also have '70 AMX hoods, which I believe are the same between Javelin and AMX in '70. So now you've got a good basic '70 body. Won't have the correct nameplates and trim and such but it'll be close.

Jimmy Flintstone sells a resin '70 Javelin bare body shell but it is a true Trans Am racer with flared fenders and no emblems.

If you start with a "cheap" distressed promo with usable glass, and you don't mind the one-piece promo (or even friction toy) chassis, you might be able to get this project together in the $60-70 range. If you need a '74 donor kit you can add another $30 at least to that. Or you can watch eBay and wait for a '70 kit or promo and pony up a C-note, or maybe two of them.

Oh, almost forgot, every once in a while a built but restorable kit comes along, too. Depending on how clean and complete it is, those can sell in the $40-$75 range or more.

So it's watch and wait, start saving your nickels and dimes. Good luck with your search!