It depends how far you want to go with it.
I did Terminator for a competition a few weeks ago and had the same problem trying to source materials. I ended up having to make a face cast to produce the prosthetic skin and added a mixture of metal shimming, latex and pieces of moulded plastic sprayed to get the right effect. The easiest bit was probably wiring up the red led eye!
It was a lot of hard work but worth it in the end as it did look good, even if I do say so myself.
Alternatively photoshop sounds good,