Well, any solar is worth having it, but RV shops are living in their own imaginary world. Take your rig and go elsewhere for solar.
Parts for 100W are commonly available for under $300 including panel, controller, nuts and bolts - everything.
Being a single low-wattage panel, it's a simple work and won't take installer more than half a day. $160-170 per hour for RV electrician job seems too steep. You should be able to find some installer to do this for $600-700 including parts and labor. You'll end up spending more time - though some installers are doing house calls.
It appears that most solar stores - AM Solar, Solar Blvd etc - keep contacts with independent installers, similarly to how hardware stores would fetch you a few phone numbers of painters, plumbers etc if you ask. Though they often have a "scratch my back/I'll scratch yours" agreement - store promotes the installer, and installer is trying to push the parts from that particular store, sometimes expensive.
Btw, 100W is way too small for fulltime boondocking. I used to do this with zero solar watts and no generator, but you might not like it. If the goal is to significantly reduce generator time, you should get at least 200-300W. With big solar arrays the parts cost under $2 per watt, including everything.