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It's not buying tokens, it's the ones you get as part of your sponsorship income. Between engines, occasionally parts perhaps and YA scouting exchanging them for money is a major part of spending them, and as long as you're not spending more than about one per race on average it's still part of a sound financial planning.

That said it's more favourable to get talent 20 drivers from the own YA, given high enough level and I'd wait 2 more in your case as it'd be likely you have to spend a lot of token getting one if trying too soon. Your driver is with 700k still on the good side though, YA ones start with about 500k of salary.
I wouldn't fire staff. Without a decent CD and TD a good driver isn't of that much use either and as you're still training your drivers the doctor is still of use as well.

In the end I'd keep that driver for a few levels and seasons, until this driver is getting too expensive the YA should be ready to then supply 2 talent 20 drivers and once those are trained the doctor gets fired. Until then token will have to fix what base and prize money lacks to pay for.

Your main sponsor pays no money for a base income but token. Those are also meant to substitute for money among their other uses. Without exchanging them you will have to run a very tight ship and bring sacrifices in your races especially during the middle levels, which in turn might put even more pressure on your financials for missing prize money and slower leveling due to racing in a lower tier.