I used a cheap 48V/400W eBay SMPSU for the steppers on a Denford star mill - with no problem; it's since been migrated into a conversion for a lathe (the star mill now sharing a control box/PSU with another mill). Yes, a big hefty toroidal transformer is better for this application but a £24 PSU will get you a long way down the road. If it gives you gip later on, replace it then. My guess is it won't do, given the size of your machine. £24 vs £100?, the volts don't care about the cost. Yes, the expensive one is likely (but not guaranteed) a better design. I'm sure it's shinier. But provided they both output the same volts then the rest of the system isn't going to mind too much.

Don't cheap-out on the rail, particularly with unsupported (supported is better!). My first router was effectively rendered useless for my intended use because of the unpredictable behaviour of unsupported rail.