Your pair will need a hutch of at least 6 x 2 x 2 (as recommended by the RWAF) to allow them to take 3 hops, stretch up fully and lie down comfortably. Mini lops will still grow to a decent size, so the 6 x 2 x 2 is not something which can be reduced. The cheapest I've ever found (while using good quality timber, appropriate mesh etc) is welfare hutches:
http://www.welfarehutches.co.uk/6ft_Single_Hutch/p1466125_10873389.aspx. There's also Boyle's pet housing who make fantastic quality products:
http://www.boylespethousing.co.uk/r...large-rabbit-hutches/single-rabbit-hutch.html.
A hutch made from timber with the correct mesh etc is always a good investment compared to cheaper, thinner hutches. They may cost less at the beginning but will need replacing within a few years, whereas the ones linked above will last longer than your rabbit as long as you keep up with cuprinol etc.
I agree that you'd be able to get a decent size second hand shed for less than the cost of a new hutch, and they tend to be a lot easier in terms of ease of cleaning out and ease of storage of various bunny things!
Do bear in mind all mesh needs to be 1 x 1/2 inch galvanised weld mesh at the largest to avoid predators.
I always feel it's worth mentioning that a combined hutch/run setup can often be cheaper than buying separately, even if you are intending to do a lot of the DIY yourself. Timber and mesh are not as cheap as they used to be!
http://www.welfarehutches.co.uk/product/6ft rabbit hutch with 4ft under run