This would be my biggest issue with using a gaming laptop, you give up a lot of control over monitoring how things work, particulary if you need to do maintenance. It's not impossible to replace parts in laptops from what I've seen but its far more complicated.
As a few other people have pointed out earlier in the thread though you can get some pretty good ITX cases now that should be quite reasonably priced.
Something a friend showed me while I was planning on my own build was the dell factory outlet too. That will be a bit of a hit or miss as far as quality goes, they are primarily custom built pcs that the order got cancelled for or that got sent out and had a minor defect that got fixed. That said though theres some very impressive prices one particular build had a £450 i7 and a GTX 770, 8gb of RAM and windows included for £600. It's an option you may want to look into but for the good deals you have to keep an eye on it and theres a large degree of risk involved, I personally went for the safer option and decided to build my own.