Honestly, I don't think you'll save a lot. If you buy the rails themselves with a threaded strip on a site like Schneidersladen, you'll pay between €14-15 for a 19" (so €28-30 for top and bottom). If, on the other hand, you buy 12U rack strips for 19", it will set you back €12 but you will still need to figure out how to mount your modules in it. For that €15, just go for real Eurorack rails and threaded strips.
I think Jim is onto something when he says to skip the 1U. I have one but it has only 2 multis and a VCA in it. Choice is much more limited. If you want to limit expense, go for 6U so you get sufficient space with just 4 rack rails.