Have a look at LAS they are only £0.70 each and one of those things you will always use, I’ve managed with 50 for the whole build and will keep hold of them as they are forever useful...
I have one suggestion- buy far more Clecos than you think you will need. You can never have too many. I'd suggest having 1/8", 5/32", & 3/16" Clecos. Nut plates sometimes use a #40 drill hole so a couple of those may be useful.