In my opinion turbo's give you way more boost. you can just feel it when you downshift and mash that peddle. for a decent TT set-up you could be spending anywhere from $1.5k for any turbo, but a twin could start around $3k.
But to actually do a good job, it could cost unreasonable prices like $9k, because it requires engine mods, labor, and correct tuning. but if you were to do it your self you could be looking around 3-6k for a twin turbo.