A/C Help

[Security guy]

My truck's an '86 Silverado with the factory air. It has the old R12 system yet and it don't work. Living in Florida, it's that time of year where it's kinda needed. I think the compressor is shot as there is oil residue on the underside of the hood where the compressor is. I know almost nothing about a/c so asking for some help. I'm wanting to convert it to the new R134a. I am mechanically inclined, so I can replace the compressor if needed and other mechanical stuff, but I don't want to get involved in charging it, etc.. Do I need a new compressor and all new components? Or is it better to take it to a shop and let them change it over for me? Any ideas on cost to change it over and get working? Any help is appreciated.. Thanks!