If you have vertical dropouts, the simplest way to convert is a White Industries eccentric ENO hub - a bit over £100 but you will also have to factor building it into a wheel.
Other options: using a chain tensioner, much cheaper but less elegant; an eccentric BB; finding a 'magic gear'.
If you have vertical dropouts, the simplest way to convert is a White Industries eccentric ENO hub - a bit over £100 but you will also have to factor building it into a wheel.
Other options: using a chain tensioner, much cheaper but less elegant; an eccentric BB; finding a 'magic gear'.
Or buy another frame as you suggest.