I was fortunate enough at another auction to pick up a sealed box of 100 rolls for £3. I was the only bidder. So the auctioneer offered me the next lot - another box of 100 rolls for the same price. So with 200 rolls to play with, I should be OK for a while.
I have zero dexterity, so reloading the film cassettes is not something I'd attempt with the lights on, let alone in the dark, which is probably preferable. But as the lab (usually) reloads the developed negs back into the cassette, I imagine it's quite easy. Having just looked at a cassette, I see there are various holes on the top and bottom of it. I imagine that if you insert a point into the appropriate one, it will open, but that's only a guess, so it should be possible to reload them.