Since your Plan B involves driving a camper to north Norway in winter the idea of doing 3 weeks in Mexico by car should not be considered offensive ? Are you dedicated motorcyclists ? Or did the question about bike rental flow from an idea that bikes being smaller than rental cars they should cost less than for a four wheel cage ? Bike rentals in Mexico are very expensive, just as they are in Europe if compared to rental cars .
If you are not revulsed by the idea of driving a car in Mexico for three weeks , I would suggest that you investigate rental cars in the DF airport .
Do a general search of bike and car rentals - easy enough just type in a Google search > alquiler de motocicletas en Mexico DF and > alquiler de carros Mexico DF and you should get loads of feed back just as I found .
Try this link .
https://www.google.com/search?q=Alqu...hrome&ie=UTF-8
Bike rentals are more indulged in by upper-crusty-tourist-riders and the rental agencies play into that demand by offering big BMWs and Harleys and so on and charging top dolllar . like $1000+ per week .
There are smaller bikes rented out in specific tourist destinations at lower prices but they seem to be restricted to riding around that particular area .Not likely that you could pick up one at the DF Airport and give it back in Cancun .
Look at these bike offerings for comparison info.
https://www.rentalmotorbike.com/es/a...otos-mexico-df
A note of caution : $ is the symbol for BOTH the Mexican PESO and the US Dollar .The prices here in this ad MAY be shocking if they are US dollars . if they represent Peso then it is less painful,
https://bikesbooking.com/es/search/?...tSameCity=true
https://www.economycarrentals.com/es...KFM_D_BwE&c=CA
After you get your head stopped spinning from this data , would it not seem more sensible to rent a cheap car to go for a three week exploratory tour of parts of Mexico . They may be had for under 20 Euros per day, less if you rent for three weeks .
You will be liberated from transporting a lot of cumbersome luggage containing your bike-riding gear and helmets . Hop in the car at the DF Airport and directly head to a hotel to get jetlag adjusted or out into the countryside . Come back ,as you say, a few years later and do it up properly on a motorcycle .
Other than perhaps reserving a hotel directly after the tiring flight do not bother to use your travel agency to book hotels for you along the way .Wing it ,keep your time of day in mind and you will have no problem finding hotels .