I'm hoping your R34 GT-T already has an intercooler.
Do you mean you want to upgrade to a FMIC (front mounted intercooler)?
Are you asking about just the cost of the parts or paying to get someone to install it for you as well?
This thread should give you an idea on install prices.
If you're wondering about parts prices, a full FMIC kit (intercooler core, pipes, hoses, clamps, brackets etc.) will set you back anywhere from around $400 (justjap or similar, maybe even cheaper), to around $600 (Greddy M-Spec, Hybrid etc) to $1k+.
You could try and see if a member would be willing to install it for you (for a bit of cash and/or some beers or something). You would get to meet another member, have a bit of fun and then you would know how it was all done should you ever want to take it off for something or install one on another car in the future. Just a suggestion. Or even find a thread showing how to install one on a GTT and have a go yourself.