another point about the middle ages: 
precious metal  was relatively scarce (obviously, how much depends on where/when) and a good part of the economy worked on produce - tipically serfs would pay in produce. 

A village could have only a handful of coins - the coins would circulate among them - whoever did not have the 'token' at the moment would have to trade produce or services. 

Thus, lending and borrowing would happen among people who dealt with larger amounts  - lords, merchants, or maybe the eventual larger scale farmer - e.g., a serf married a serf heiress, then his son got a double sized farm, and so on, eventually he has to hire people. 
So, dont expect "Joe the smallest serf" borrowing often, even small quantities.