A good electric bicycle costs around $3000. The corresponding rent should be 30-50€ per day.
a) Bring your own bike by plane. The electric support an US bike is limited to 32km/h (20mi), not only 25km/h.
b) You can buy a cheap bicycle in Decathlon(.pt/.es). If it breaks, go to another Decathlon store and complain. If it is still OK in Santiago give it to a student in Santiago or someone else who can use it.
Expect to charge the battery of Decathlon bikes 2 or 3 times a day!
c) Use Google! First link for Lisbon:
https://www.lisbonbikerentals.com
On the Caminho you will not pass an altitude of 500m. Keep along rivers, old train lines and the Sea to avoid hills. Wind might be a problem on the coast, but you have to die one death.
Food is inexpensive and usually with a beverage included. Choose your own. Eat where the locals are.
There are still public open air washing places in Portugal, but it is easier to use the service of a washing machine in albergues and hostels. For the ~600km even slow cyclists with only 3-4hours/day pushing need less than two weeks. So what are you worrying about?