The hi-res mats, both DAZ and Vendors, are more expensive because they're more work.  For V3 there are only three templates to work on, the head, body and teeth-gums.  For V4 there are 7 now so it takes a lot more work to make sure everything is seamless.  

I'm working on a set for her right now and have been since I got her.   It takes a lot of work to blend textures and ensure no seams.

Hugz from Phoenix, USA

Victoria

Remember, sometimes the dragon wins. Correction: MOST times.