My 6U 104 hp TipTop Audio case was only 300 GBP, no custom building or time wasting needed.
I have already out grown this size within a month or 2 though, a 9U 126 hp or 168 hp is what I will need eventually I think, but for now not so worried about it because its pretty safe to say 2 out of the 3 rows will be filled with sequencers, clocks, utilities and the likes.
It just depends what you want to do and how you want to go about it, but for your case it sounds like a pre made case might be a better choice for you.
My Eurorack has been sitting idle for months while I slowly buy a bunch of modules that will allow me to make sounds. Live performing, sequencing and extra utilities is for the future.
Some recommendations would be a Doepfer case, TipTop Audio Mantis, or some other not so large 3U or 6U case you should be able to pick up for 300 EUR more or less.
Its probably not the best idea to dive into eurorack just yet if your budget is that tight, for me I have personally accepted being homeless in turn for owning a Eurorack, loving it.
Doepfer has a DIY PSU kit aswell:
http://www.doepfer.de/a100_DIY_kits