Assuming VFM are important, Kart racing.
IMO most normal road cars are just not that much fun on track. eg. I attended a VXR day last year. Yes it was good as they go, but I was still conscious of being in a barge most of the time.
The single seater experiences are more raw, but are now faced with far more safety and noise regulations than there used to me, limiting the ability to have a real play.
Kart racing in a decent pro-kart is IMO easily the cheapest way to enjoy some serious on the limit stuff.