re: How much would it cost to keep the Hubble in service?
Quite.
It would be considerably cheaper to launch a replacement (see Hubble Origins Probe)
The benefits of Hubble are reducing - look at the work from Keck et.al now - matching Hubble in some wavelengths.
I'd rather they just whacked a de-orbit stage on remotely, perhaps with some plugin power capacity and gyros to extend mission for a little while, but it's just not worth bothering about that much imho.
Doug