2 swiftech xt = $150
additonal pump+reservoir = $100
additional radiator = $40
TEC = $25
Total ~ $315 + time
You are right it's not quite worth it, in some sense. I'm building a 4 TEC chiller, and I found it costs much more. I guess TEC stuff never justify their cost... You can see much crazier things, people don't really care about the cost or time when come to extreme cooling, just have fun
In the end I could sell those swiftech xt.
Once you're looking at TEC cooling, I think it's fairly safe to assume that efficiency and performance aren't what you're looking for...
If you want cost effective get a rasa kit and some GPU blocks and spend the rest on better hardware. Beyond that any additional cooling wont provide bang for buck