Considering how much a canned tune can cost, and just how little they do for you, its not worth the investment.
Even for a 3.4 setup, just scan for knock and adjust pulley size/octane to compensate. Stock tune is good enough.
Now if you want a dyno tune, expect to pay $100 in credits, $50-100 per hour of dyno time plus the fee for tuning.
Depending on their qualifications and typical rate of pay, some tuners charge more and get it. Quite frankly, there are a few out there that deserve it too. But those are few and far between.
Don't jump and say dyno > street or street> dyno. There are distinct advantages to both.
Unless you're willing to learn and teach yourself, tuning your own car probably isn't for you.
Z34 guy: HPT always requires credits unless that "group" has been unlocked. Most shops wont have 3800s unlocked unless they're intense/ZZP/PRJ/Overkill etc. They'll likely have gen III V8's unlocked, but that won't help you.
HPT will let you adjust the basic things but if you're really in need of a tune requiring special attention, then DHP would be preferred despite being more difficult to use and less reliable.
And more to the point, the P04/P05 (the PCMs our cars utilize) are so simple there isn't much to change. Also trying to determine the appropriate timing/pulley to run, granted you're not seeing knock, without a dyno is a guess at best.