But you just trying getting observing time on those!

GALEX has much lower resolution than HST (4" vs. 0.02"). The now-dead ACS still has the best resolution for any optical to near-UV camera in operation, in space or on the ground (though ESO is getting pretty close)

I was at a talk about some of the JDEM missions, and they brought up the observing time/cost comparison: with a ground-based telescope, you've got at *best* less than half the year available for observing (night), and even at the best sites, usually more like 1/5 or less, due to bad weather and seeing. So a space-based telescope can do a lot more observations in a given amount of time. So if a space telescope costs 10x as much, and runs for the same amount of time, it is still a decent value, monetarily.

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