You're going to struggle to find anything G1 accurate that scales with Masterpiece figures without actually buying Masterpiece figures.
If you don't want to break the bank on MP figures, the Classics/Universe/Generations/RTS lines are probably your best bet, though even then some of those figures can be very expensive.

Grimlock: You can pick up the recent FoC Grimlock relatively cheaply. He doesn't look much like his G1 counterpart and he doesn't scale with MP10 very well either, but there is a third party upgrade kit that will at least give him a G1 accurate head. Otherwise G1 and Masterpiece are your options.

Inferno: You can pick up Universe Inferno for ~US$60 on eBay. I don't know of any other realistic options.

Bumblebee: You can probably pick up the RTS Bumblebee very cheaply which is an updated G1 look (different car mode), or alternatively the new Generations Bumblebee is an option (also cheap), but not even remotely G1.

Soundwave: Short of the G1 and MP figures there isn't a good G1 accurate representation of Soundwave. The recent WFC and FoC figures might interest you, but I'm not a big fan of either of them. Music Label Soundwave would be a good option, but for the price you're probably better off just paying a little extra and buying the MP figure instead.

Ironhide: BBTS (Big Bad Toy Store) carries PP05P which is the only G1 accurate Ironhide available. It's US$99 and is really more suited to the CHUGs line, but can just about pass next to MP figures. It's kind of a nightmare to transform though and I'm not sure how well suited it would be for your son.

Ratchet: I don't think there's any reasonably affordable option for Ratchet. You could pick up the Transformers Prime figure, but he doesn't really resemble his G1 self very closely at all.

Ravage: The Hasbro MP Soundwave is the best place to get this guy. There are some third party options that aren't as good, and a version of him also came packed in with Classics Hound (again an average version of him). Takara are re-releasing Hound soon, but I'm not sure if he'll still come with Ravage.

Jazz: The RTS Jazz figure is pretty awesome and the best option, though he's not really accurate to G1, but rather an updated version of G1 Jazz.

Omega Supreme: There's an extremely expensive third party Omega Supreme and the not quite so expensive, but still expensive, Year of the Snake Omega Supreme re-issue. Neither is very accurate to G1, but those are pretty much your only options short of the original G1 toy.

Perceptor: The RTS figure is very nice, but not that close to his G1 counterpart. He transforms into some kind of "Sciencey" Exploratory Vehicle.