zcarm :
Honestly, once you take off the stock cooler the graphics cards are just about the same. I would just get one with a super cheap air cooler that you wouldn't mind pitching. Here is the cheapest 980 ti I found on newegg:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814500376&cm_re=980_ti-_-14-500-376-_-Product
But honestly you could look at other websites. Since most of the time when you pay extra you pay for either A. factory Overclocking (that you can probably do yourself if you are watercooling) and B. The cooler. Other than that, there isn't much difference. So my recommendation would be to go as cheaply as possible.
Honestly this. While higher priced custom cards may claim to have higher quality ASICS (i.e. better silicon, better overclocking), there is no guarantee on quality from the manufacturer. I haven't heard of any 980 Ti that wasn't a great OC preformer, so I'd go cheapest reference and put a block on it.
BTW, my EVGA 980 Ti has an ASIC quality of 84.6% if that means anything to you.