Wheels are quite variable for an unfashionable wheel-size, but the Pro 2 hubs have some value still for sure. I keep an eye out for a 26er rear wheel and rear wheels with Hope hubs will sell for £100+ easily enough.
Forks are possibly quite valuable as they’re less easy to get hold of these days, but for something 10+ years old I’d imagine maybe £150 (based on my own 2012 26er REBAs :-).
So IMO market value is maybe £250-300, something of that order.
How you work that out with your mate is up to you, but I would echo what others have said about payment of some kind being “a done deal”.