I think you might want something built rather to your specs than buy someone prebuilt system to there specs.
I can build you one for cheap labor and parts. A mini will run about $400-$500
a full like flex atx probaly around $300-$400 mabe less on what I can find. This will be a quality system no just thrown together , I do ths for a living and I can send you pics of systems Ive done.