series for under £10k...

[kickstart]

Tring not to be cynical it is all about money. You could use FVee as a springboard to whatever you liked provided you find the money. Having once worked for a company that sponsored a driver about 20 years ago, I really do not think it matters to the sponsor what previous experience the driver has had unless you are looking for a big budget for F3, BTCC etc. But if a sponsor is looking for a proven race winner at this level then there will always be several options not including contacting the top teams themselves.
Raising serious money for motorsport at a level below F1 or BTCC is in my view almost impossible unless you have a personal connection with an individual or company. That is why so much sponsorship is tied to a particular driver eg the Verstappen saga at Jordan.
Acf8181 - enjoy you motor racing but if you want to get somewhere you really have to be in it to win it.
Good luck