The following is from someone who has an Obutto Revolution cockpit + TX base + GT leather addon + T3PA +TH8A shifter and an XBox One with FM5, FM6, FH2, Project CARS & Dirt Rally.
FH3 is IMO already a very solid choice, I pre-ordered it as well and I’m looking forward to it a lot. But, you don’t need a wheel for it, the controller is hands down the better input device. All Forza franchise games poor to mediocre wheel support at best.
FM6 I liked a lot in the beginning, when it’s new it really draws you in mainly due to the great level of polish in the game. It’s a struggle with a wheel but it can be done, just don’t expect too much realistic behaviour. The controller is here as well the best input device as you can never oversteer (something that happens a lot in an unrealistic way with a wheel). On the pro side FM6 has hands down and by far the best car grid out there of any current gen racing game. The graphics are great as well and the track count can sure hold its own even though for my taste there are far too many USA based tracks. But I guess that counts for all rivalling games since the GT series is more focused on Japanese tracks, Project CARS on British tracks and Assetto Corsa on Italian tracks.
FM6 is no sim though, let that be something very clear. Poor ffb code, poor car division grouping, rewind buttons, wheel spins, unrealistic tuning upgrades, it all feels like it wants to look like a sim but it has these arcade hand-holding features all over the place. But it’s fun to mess around with on a controller. Since you seem to be short on money and doubting what to get, at least give the FM6 demo a try so you can see for yourself.
if you want a sim-like experience as good as it gets on a console then I recommend Project CARS or to wait for Assetto Corsa. From what I’ve read about the PC reviews they both hold their own. I’m personally playing Project CARS a lot and what I really like compared to FM6 is the much better singleplayer campaign (racing calender with championships), much better and realistic grid lineups per race (not this random PI grouped races like you see in FM6 where you can easily have a classic GP car, an SUV, a sports car and a race car all in the same race), dynamic weather effects that influence pit strategies and tyre choices and then also some extra fluff like helmet camera, motion blur, bloom, FOV adjustment and overall a highly customisable game (you can even install a telemetry app on your iPad and mount it next to your wheel).
If your 30 bucks means chosing between the FM6 base game or the Project CARS GOTY edition I would go for the latter.
FM6 : high level of polish, most diverse car selection including Porsche (addon) & Ferrari , best graphics, newbie friendly, officially licenced cars (V8 supercars, Formula E, NASCAR (addon).
Project CARS : more realistic experience, best with a wheel, best lighting & day/night effects, dynamic weather with pit tyre strategies, singleplayer racing calendar with championships, best customisation.
They are really two different games, I can’t make the chose for you, only give my advice. I would also advice to watch a lot of YouTube gameplay videos if you’re in doubt.
Waiting for Assetto Corsa sure is another possibility as well, if you are heavily into multiplayer I would even recommend that. The Project CARS multiplayer community is much bigger on PC than on both consoles. On PS4 it’s more popular than on XBox as well.
Then there is also Dirt Rally. I never played a rally game before and I was extremely pleasantly surprised with it. It doesn’t have a very long replay value for me (the stages do get repetitive after a while or maybe I just like circuit racing a lot more) but the level of immersion and realism is truly outstanding. You want the best ffb from your wheel? The best graphics and car sound? Give Dirt Rally a try.