Forest Green Rovers, my local team when I lived in England, built a new stadium in 2003. It cost about 5.5 million in today's money.
It only has 2 stands (for about 5,000) capacity, so would cost a few more million to add the other two.
As part of the construction, they also built a gym, a leisure club, a sauna, a pub and meeting facilities - so it's in use 7 days a week.
Because the owner is a bit of an eco-fanatic, it is a sustainable design with an organic football pitch, and solar panels on the roof of the stadium to power 25 per cent of the stadium.
The pitch also collects rainwater to be recycled around the stadium and all waste cooking oil at the club is recycled into biofuel. The club introduced a solar powered 'MowBot' in April 2012 which cuts the grass on the pitch.
Local farmers use the grass cuttings from the stadium to condition their soil. The area outside the stadium has also been developed into a habitat for wildlife through the planting of wild flowers and native trees.
We might not need all the eco-features, but a 4 stand version something like that could be just the ticket.
(if they could replicate my favourite local pub, The Ram in Woodchester (400 years old, beer from the local brewery) they'd have a goldmine on their hands).