I'd swap but I'd expect cash as well.
Your YBR is worth around £1300-1400 depending on mileage and condition (going on average of ones that actually sold on eBay recently, private sales no dealers).
His Divi is worth less than £1000, unless it is literally pristine in which case maybe £1100 tops. Plenty sold for 500-600 quid with MOT and Tax (Again worked out same way as above).
Say the YBR is reasonably clean and his average I'd be wanting at least £400 notes my way with the swap and he would still be getting a good deal.
