Many (Euro and Canadian) cities now have short-term bike rental programs. If you keep individual trips short, these can be free, since usually you don't pay for the first 20 minutes. Ride it, park it, walk around, ride back, park it. Paris does this with both bikes and cars, even.
Bike rental is hardly ever good value: but it's hard to be sure you can find a used bike to buy that fit and meets your needs, via Craigslist or equivalent, for a short stay. But even buying new and then bringing the bike home can be a better deal. One idea is to contact a bike rental place and ask if they can sell you one of their used rental bikes: buy it cheap, ride it, then sell it or bring it home to keep or sell.
I do know people who've lined up cheap used car ads, all the best prospects, then spent one day buying used and driving that car for a month or so before selling it and coming home. Takes a bit more paperwork though: license, insurance etc.. (This is one clear case where research and legwork, and language skills, can substitute for spending.) I bought a used Peugeot in France, drove it 1000k to Italy next day, then drove it on summer visits for over 4 years. No problems. Way cheaper than renting.
A lesson here is that longer trips might lend themselves more to such ideas than shorter trips.