The Elan Valley hotel itself does not have any available rooms but are plenty of places nearby to stay, the places listed below are in the nearest town, Rhayader, and is a 5 minute drive from the venue:
The following hotels have come recommended:
There is also booking.com and Laterooms of course! (Links are already set to go to Rhayader)
If you have a campervan/motorhome:
You can stay at the Elan Valley Hotel for £5 per night
If you have a caravan:
Elan Oaks is across the road from the venue