Recommendations for unrestricted single seater experience

[notax]

I regularly arrange driving days for clients, generally 'supercar' days. Recently took 3 clients to 6th Gear Experience and we were all very impressed. I now have a client who would like to try a non restricted, single seater experience. He and I have both had a go in various limited Formula Fords and found the experience very underwhelming.

My budget is about £500 and I'd ideally like to arrange for him to drive an unrestricted Formula 3 or equivalent. He is an experienced driver with his own track car and wants to experience a fast single seater. Any recommendations appreciated.