existing car-kit with which bluetooth adapter?

Hi,

two years ago I installed a THB car kit to work with my nokia 6310i. Now
I have a Sony Ericsson T610.

Could somebody share some thoughts about Bluetooth-Adapters, that can be
used in combination with existing car kits?

I know, that THB offers one, but just as expensive as buying a new
bluetooth car kit. Then there is Lintech. They have one, too.

Are there any other Bluetooth-Adapters?

Thanks,
Sascha