I'd say between £80-120 on a good day mate, the Alias was considered one of the most desirable of the 05 models, being as its an 'old' marker even with the aftermarket parts, don't expect it to fetch decent amount, as It's only going to be desirable to somebody who's probably owned one years ago and would like one purely for sentimental reasons or a back-up gun.
Timmy's ruled the roost prior to the ego 05 being released so a good marker but parts in the UK will be very difficult to find for the new owner.
hope this helps mate