(I know nothing of the 15mm historicals scene, I hope you're not offended!)

I would also suggest using figure painting services as a rough guide. A quick flick through some sites suggests approximately £1.25 per infantry, £2 per cavalry and £6 per elephant, with ~50p per base. Checking the photos I think you have

~16x4 spear = £80 to £88
~8x3 Light inf = £30 to £34
~16x2 skirms = £40 to £48
~6x2 light cav = £24 to £27
~4x ele = £24
~3x4 bolts = £15 to £16.50

Giving a total for a painting service of ~£213 to ~£237.50

Allow a discount on that for wear ant tear, 2nd hand etc and you aould probably be looking around £150 for a quick sale, to £180+ depending on condition, painting quality, desirability etc. For example, are all the weapons complete, are they varnished, is the painting shaded etc.
And then you have to consider transportation - are you selling their 'box', are they magnabased, how will you ship them etc. all of which should be considered in the price

If you are considering a 'Bring and Buy', I would advise against asking more than £200 (or 200€) purely for psychological reasons etc, though you may find that they can assist in judging the quality and desirability.

Final thought is what rules are they intended for. I don't play FOG or DBMM, but if they can be fielded without rebasing, that will be a bonus - if not, then that might also affect their price.