Depending on what radio and how much the harness will be...You will be into it for well more than $65. Even a cheap head unit will cost around $100.
Just quickly looking on crutchfield for just a radio with bluetooth streaming capabilities, that is $80, $9 for the trim install piece, and another $65 just for the wiring harness to keep all the bose and bluetooth working. You most definitely can get the stuff cheaper, but you won't be plug and play like that. Or if you know a shop that has either a TechII or some other scanner/programmer (saw that snap-on tool works, but you have to pay for the software from GM).
If you like to do wiring and tinkering with your truck and you have the time, you can get an aftermarket radio to work...but you already have a stock unit that you probably might break even if you try to sell it. I would call the dealer and see how much they charge to unlock the radio.
2016 GMC Sierra 2500HD Denali
Extang Blackmax Tonneau
Weathertech floor mats and mud flaps
X-pel clear bra
295/60-20 Toyo Open Country A/T II
Custom EFILive tuning by Kennedy Diesel
Kryponite UCA and Bilstein 5100s
SOLD 2004 GMC Sierra LB7