I don't think you would need to pay anything to develop the CLAM client. It is open source.

We only really had one developer (xploited) and he seems to have lost interest in working on it. He was in the process of merging a more recent release of the Bitcoin client into the CLAM repository, but it's a big job and I don't know whether it's in a state that is safe to release or not. You can find it in his github repository. It is quite possible that it is working fine, but I think it needs more testing before being released.