Gee £900 i did well then sold mine for much more than that, 5 years old is classed as nearly new with trailers. I would say anything from £2000 to £2300 but then i dont know anything about pegasus trailers.
I paid £2200 for a 5 year old Ifor Williams 510 last year. If the pegasus trailer would take 2 X 17hh I would have paid £2500 for one. I would have thought it would be worth around £2000.