Not a difficult job and probably DIY if you want. Your shaft coupler could be 2 different options. The first is keyed with a set-screw... this is the easiest one... unbolt the coupler from the tranny, remove the set screw and you should be able to pull the shaft straight out and inspect the keyway on the shaft and coupler for damage.
The second option is the newer style that has a lock nut on the end closest to the tranny. Unbolt the coupler, remove the locknut (you may have to cut a socket down to fit in the narrow gap between the tranny and the coupler, but it DOES NOT require that you remove the tranny.) Again, once removed inspect the keyways for wear/damage. These should be TIGHT.
If you have the old style/set-screw coupler and it's worn, I'd recommend you have the propshaft replaced and upgrade to the newer style coupler.
If the prop shaft is bent (roll it on a piece of glass) you can either have it straightened or replaced. If it's bent... when you replace/reinstall it make extra sure that you align the engine to the coupler (there's a good thread at supraboats.com/bbs), pull the strut and have it checked, and replace the strut bearings.
Don't ask me how I know all this.
Also... Marine Associates (http://www.marineassociates.com/
) was (likely) the original OEM on the propshaft/strut/couplers and can save you some money on repair/replacement on any of them. I'm lucky enough to live really close by and have had them fix/refurb my entire running gear over the years.