We have a few other hidden upload limits, and we'll probably use ads later on to solve the financial issues, but right now we're trying to estimate the interrest of the service in general.
Actually, they're not that expensive. The .st TLD is maintained by Bahnhof, a Swedish internet provider ( they are actually pretty cheap. Check out www.nic.st , they cost about 45USD/Year there).
They will be stored until they're not downloaded for a year or so. We'll calibrate the parameters along the journey, so I really can't say right now, but we'll definately let you guys know!