The DSE price of $400 is for the pair. The $80 you quoted for the factory inner wheel house is for each, so make that $160. But anyways, it's up to you how much you want to cut and weld, there are plenty of guys fabbing their own.
The extra money I spent for DSE tubs was well worth it in my time alone. If you're going to mini-tub, the less time you have to spend in the trunk the better.
I did mine using new inners and some 18 gauge years before the Deep Tubs were availale, the way DSE used to do it...it easily doubled the time it took to do the mini-tub job...next time I will use the DSE tubs for sure!!