Cinque Terres

Given the hillside nature of the towns and prevalence of cobblestone paving, a wheelchair is not a feasible means/mode of moving around the villages.

if there is a wheelchair service I would absolutely expect there to be a fee.

Are you making a cruise ship stop? If so, probably best to see what the cruise line offers, to see if there is anything suitable.

There may be accessible vans/drivers that could be hired from la Spezia, at a cost, of course; but I have never heard of wheelchair services within the villages. You will get a good idea of the wheelchair challenges if you watch any of the many YouTube videos of the CT. This article is written by a wheelchair traveller who has visited there: https://www.sagetraveling.com/cinque-terre-disabled-access

Long story short, the CT is probably amongst the least accessible areas in Italy.

I don't think any of the five towns are well suited for wheelchair access, although Monterosso is relatively flat and paved so you could tour both sections of town although you may have some difficulty going too far up Via Roma in the old town. Getting to Monterosso would have to be via a wheelchair vehicle as you wouldn't be able to use the trains. You'd have to arrive via the "new town" road as the "old town" carpark is on a hill so not as practical. I don't see any way you could access the ferries as passengers board via a narrow ramp on the bow.

We plan to do a water tour of the villages, in addition to walking the trails and perhaps visiting via train. Water tours should be a great way for the mobility-challenged to enjoy the area.

We plan to do a water tour of the villages....

Just a mention that the commercial CT ferries aren't wheelchair accessible; the narrow ramps can't handle them, and there can be some steep stairs to the boarding areas in some of the villages. Example in the link:
https://goodtitevs.best/product_details/36752816.html

Your best bet if wanting water views would be a private tour, such as the one mentioned in the previous link.

Sage Travel was mentioned above, and it looks like they offer (or may offer) an accessible tour from La Spezia.
https://www.sagetraveling.com/Highlitghts-of-cinque-terre-accessible-shore-excursion

Thanks to all of you who responded to my post regarding wheelchair access in Cinque Terres. Barbara