Here are the two being talked about. You can probably get the GP4K's a little cheaper form the UK, but you will wait weeks to get them.

Pro 4 $71.99 for the set shipped http://www.ebay.com/itm/140931926387...84.m1497.l2649

GP4K $81.95 for the set shipped http://www.ebay.com/itm/2-x-Continen...item415d26cf05

I have also tried these and had good experiences

Michelin Lithion 2 $55.85 for the set shipped http://www.ebay.com/itm/2-x-Michelin...item3380dd8d82