My issue with this is not what you are charging, it is your lack of community spirit.
I gave you a good deal, you should pass that good deal on in a similar way.
I could have got much more for them too, but in the spirit of the community I gave someone (who, as it turns out is somewhat ungrateful) a good deal and you are simply trying to make as much money as you can.
Also, they are now much more used. When you bought them from me they had been used for a couple of hours on an indoor track. You used them for 3 months through the winter and spring to commute and want back more money than you paid!
+1
One good turn deserves another