My suggestion is that if your mum is concerned about you building your own and won't have it, take her to reasonable PC specialist shop and speak to the guys there and see if they will be able to build you one or even have a system currently built which will suit because you have been taken for a ride BIG TIME..
I don't have a problem with ALIENWARE gear, but when they charge you this much for a PC!!! It is ridiculous, I can understand why people might not feel confident enough to build their own PC but going to your local PC specialist shop will be alot better.
Take your mum to the shop, talk things over with the guy at the counter most shops will variable payment plans such as leasing and will offer a very good warranty and services plan. Cos for that cash they will offer a lot better.
What area are you from? (if you don't mind me asking...)