You can buy said belts for about $20-25 at your local parts store, maybe less. Call a couple of quick lubes - I wouldn't pay more than $60 for this service. On most cars it's not a difficult DIY job. Take a look on YouTube for guidance, then decide if it's your cup o' tea.
Depending on the brand and where. I have paid $35 to $50 for the belt. I think the dayco poly rib Im running was $44 @ pep-boys.
BTW, the dayco poly rib @ 1/2" shorter. Has been the best on my gen1. No slipping on the power steering pump. Even on hard acceleration. All others did.
Oops, I may have underestimated. I do my own though. O'Reilly showing three choices: MasterPro $19.99, Gates $29.99, Motorcraft $37.99. Most fast lube techs can put one on in five minutes or less, most cars. Hack mechanic like me a few more.
Serpentine belt is fairly simple to replace. I ordered a great Good Year Poly-V belt online for 14.95 with shipping and it took me all but 20 minutes to remove the old belt and replace with the new one.