You might would like the Infinite CLT RDA, I was more pleased with it as far as build quality than most of my cloned RDA's, and it's a dual positive block on the center post I believe. I have the Infinite CLT which is authentic, even though it's a few other designs cloned into one, but infinite is the authentic maker. There's probably clones unfortunately so if you do get it, I can't recommend a cloned one as I have only had and used the original. I think it runs about $30 brand new for the authentic one, and there's a V2 out now that looks really nice.
You might check out vapingwalrus.com and see what they have, they're one of my favorite vendors for buying clones because they have EXCELLENT support, they really take care of their customers. And they're very honest and upfront. If I email them asking about a particular RDA and it's quality, they'll tell me that it's built pretty good, or if not they'll say something like "Unfortunately I've seen a few problems with these, if it's build quality you want, we have product x and product y that are built really well and have the features you wanted"
Edit: Here's a link to the CLT V2 info with a discount code, make sure the discount code is still live though since I don't know how long they were offering that deal, still a good price/good read at least either way
http://vapingcheap.com/clt-v2-rda-by-infinite/