I always use ebay and filter for sold (not completed) items. If theres a few, average them up.
eBay prices are just random though…
I often track stuff and then see a used component selling for more than a new item that can be purchased right now. (not even being sophisticated but just using the google shopping search) then inexplicably there will be some complete bargains.
It’s interesting because I don’t stand to benefit because I was planning to use the components on the new frame (except wheels since new frame is not QR). The sale of the bike as a whole will probably leave me short by a few quid but I’ll have the benefit of a new groupset funded by the sale. But I’m keen to sell it a fair price to a friend so I don’t mind.
…..
He definitely wants a ready to ride bike.
If its a good friend I’d price up what its going to cost you excepting the frame including any discounts and split the difference? Does he really want the carbon fork for example … and presumably you do…is there a different saddle/seatpost on 50% discount at the moment?
The point really is you should both gain from this… and it shouldn’t cost you money above a new frame but he shouldn’t be funding it either. If you price up as if you are billing 2 bikes with possibly different price options then just work through various options…
In practice I’d think that you’re working towards buying all the parts for the new frame and sticking them on the old frame but then just agree its not worth perhaps doing the headset and replacing a crown race for example?
It’s totally possible that the price is not working but then you are left with selling the frame used but at least neither of you got ripped off.