Fast prime for indoors. Suggestions please.

I visited a historic home/estate on Sunday, & while photographs were permitted inside the main mansion, flash was not. My 15-85 on a 7D was just not up to the task as most rooms had pretty low lighting. Tripod not allowed due to volume of people, so high ISO's were all I could do to try & get reasonable results. I really don't like going high, but a lot of the time I was forced to go up to 1600 & beyond. My 50f/1.8 would have done for some shots in the larger rooms, [I left it at home unfortunately!] but something like a 24/30 f/1.8-f/2 would be perfect for the rest. I have looked at Canon & Sigmas offerings, & have a budget of about £250-300. Any suggestions? Thank's.

--
lee uk.
There are old pilots, & there are bold pilots, but there are no old bold pilots.