No tool really, just market research. Look at enough bikes for sale on forums, ebay, gumtree etc and you’ll get an idea. But it takes time to get a proper sense because many (especially ebay and gumtree) are overpriced and don’t sell, so that advertised price isn’t indicative.
On this forum bikes are usually a bit cheaper than ebay because we’re happier to sell here to people we either know or know will be reliable and we look after each other a bit. BNA forums is a bit more overpriced but could give you a good sense for carbon roadies.
Ultimately, if you have some time, try putting it up at a price you’d feel happy with and see what responses you get. If it doesn’t sell, drop the price a bit. The Ridley you’ll get some interest from on BNA. The Colossi you’ll get some interest here no doubt.
EDIT: and probably, as a sort-of-rule, about 50% of what it would cost to buy new or build is usually about where things end up, subject to just how good condition it is in. But that is where you may end up, and it could sell for more, especially if it’s a bit unusual and sought after.
Thanks for the replies. I just took some photos, hard to find a decent back drop though.
Taking a look BNA forums and trying to find a similar specd roadie.
I would split it but Ive always been so awful with bike mechanics I don’t trust myself
Example this one time I ruined the threading on the crank where the pedal goes because I screwed it in the wrong way.
Had to find a lbs who could rethread it hahaha
Half the cheapest (new) online price for the same or a similar item is a good place to start - adjust depending on the percieved value (i.e when njs was hot vs now). Then adjust again depending you want to haggle, want a quick sale or snag an impulse sale.