yeah sure mate, I know what you mean there...very tough to sand back a brand new one...and also, I noticed too that $70 was about the lowest...For what it's worth, I've had my wife hand paint a couple of sopranos for me...and all I did was buy a cheap mahalo for $19.95 and use that...a plain wooden one...you could always buy a couple of them if it's your first go at handpainting...just to find your feet and technique...get used to working with the dimensions, how to seal it properly etc etc...use 'em as "experiments" then once that's sorted you could go with a better quality uke - 2nd hand or otherwise- knowing exactly where you're at with it and how to do it right.
even still, there are probably a fair few UU members out there who may be able to help you with exactly what you're after right now, once they get a hold of this thread...