£1000 sounds a lot, if it's just for the sessions and doesn't also cover recorded music. According to PRS's Tariff P, for up to 100 people the charge should be £7.92 per event - £411.84 pa for a weekly session. Still too much if much of the music is not actually controlled by PRS (usually the case at a folk session), but a lot less than they're quoting.

The problem is, in situations like this the landlord often isn't interested in getting into prolonged negotiations with PRS for something which probably doesn't bring in very much extra business, and so they stop the music. Everyone loses out, including PRS's members.