Less extravagant than some others here, Nene Park is a favorite of mine. It's formerly the home of Rushden & Diamonds (R.I.P.) and the current ground of Kettering Town. http://en.wikipedia.org/wiki/Nene_Park "...holds 6,441, with 4,641 seated and 1,800 standing. The car park can hold 800 vehicles." http://www.thediamondsfc.com/page/NenePark/0,,10784,00.html
Wiki says 30 million pounds built in 1969, I assume the 30 mil are what the cost would be today not back in 1969.
Proposed temporary stadium for the CSI flames (Tampa bay) http://www.vsi-stadium.com/development-projects/modular-temporary-stadium