In anticipation of this being moved to the appraisal section. You'd probably get about £125 for the gun itself, looks like a cheap red dot, extra mags a batteries add very little to the value. So like £150 all incl' possible slightly more if you're lucky.
Quick search tells me RRP is around the £200 mark.
But, what you would get for it used obviously depends on the condition.
No idea what the vest thing / mask is that you mentioned, haven't seen the magazines, so can't comment on that.
Also the above discussion regarding if it has been converted to use gas / HPA is going to make a difference but looks like it is just standard.
Just to add, finally it might be useful to know if you sold it & wanted to post it they generally don't allow batteries so they might not be able to include those anyway, and again price depends on exactly what they are and a lot of people usually have a collection of them so not sure how sought after they would be