Typically, if you can't do the work yourself, it isn't worth removing the base plates. With that said, some are easier than others. My GMC Canyon required removing the entire front bumper assembly and took several hours to install, yet my Ford Raptor install required just a few simple bolt holes and no removing of parts.
When you look up base plates on Etrailer, they typically have an install video available for each baseplate model. Watch the one on your Terrain and see if it looks like it's easy or difficult. That will give you an idea of how much it might cost.
Used baseplates are only valuable if they're for a commonly towed vehicle. I typically remove mine because I do my onw work and I know how they went on. I'm still sitting on a pair of Roadmaster base plates for a 2011 -2013 Chevrolet Silverado, which is popular, but no bites when advertised.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor