The only hard part about the turbo is having someone manufacture a decent turbo manifold and getting the piggyback ECU unit tuned.
Everything else is easy to purchase or have it made, just that damn manifold sucks.
Piggyback I would suggest Split Second FTC1-E unit, and this unit should not be a problem just takes awhile to tune it on a Celica because it needs a lot of dyno time to get the tuning done right.
If you want an estimate... I would say around $5000~$6000 for a custom setup that will run well. This is when I would just recommand you to get one off David Draper when his turbo kit comes out because it is a lot cheaper and well thought out kit