Bog standard? if you mean a mass produced cheapy made from laminate then not more than £40. I recently bought a Spanish luthier made acoustic with a solid cedar top (small bash in upper bout) for £21 on ebay. The more detail you can give the more you will get for it. The following info. will help
Make/model/serial No.
Style: Folk,jumbo, dreadnought,parlour,cutaway, classical, acousti/electric,
Top, solid or laminate?
Body, solid or laminate
Strings, steel ,nylon (need replacing?)
String height at 12th fret
String height at nut
Fretboard width of at nut, straightness, amount of dip or bow
Tuner type; spanish, open or sealed.
General condition of finish such as scratches and blemishes
Study similar ones on ebay, there are thousands to look through.