Martin,
thanks for the link, I have already done a lot of reading about high performance thermoplastics. I will be prototyping some home made blocks in a couple of weeks.

The materials I will be using : black UV stabilized Polyacetal (55-60 MPA tensile breaking strenght, manufacturer -Ensinger), glass reinforced nylon (Polyamide 66, gf30%, 160-140 MPa tensile breaking strenght, Ensinger) and graphyte impregnated PTFE from Fluorocarbon UK.

The expected price for the test block is about 4 Euros/56mm sheave block.

PEEK (plain) costs 205 Euros/kg (VAT excluded)
Polyacetal costs 8 Euros/kg
Polyamide 66 GF30% costs 15 Euros/kg

I think the combination of expensive materials+exclusive design is what makes the Karver blocks so expensive.
I don't think they are interested in the small boat market at all.

BTW -the price tag from wiki is not at all accurate. The price I got was from industrial suppliers from Europe.