If you're willing to risk it, I've seen Motherboards on eBay that meet your specifications for as little as 47.00 GBP. Search "Brand NEW SEALED GIGABYTE 970A-DS3, AM3+ (plus), AMD CROSSFIRE Motherboard". It's "Buy it now" so that's the price you'll pay (before shipping costs).
Scan.co.uk have a Quad Crossfire model ( M5A97 R2.0 AMD 970 Asus AM3+ ) for 67.86 including UK VAT ( Value Aded Tax ). That's before shipping costs are factored.
There's also a Gigabyte GA-970A-DS3P on eBay listed as 'as new but cosmetically used condition'. That's 39.99. Search "Gigabyte GA-970A-DS3P Socket AM3+ FX/Phenom 2 Motherboard".