My club is looking for a free, or very low cost, booking system.

We want something with an easy web-interface so that everyone can use
it, including old farts ;-).

Suggestions ?

What you're looking for is very simple from a programming point-of-view.
This is the sort of thing you could take to a computer science student
at the local university and ask him to implement it for a few grains of
rice. That might be more than you're willing to offer though so there
are several projects I have been able to find online:

http://www.shezhu.org/
http://jroger.nuxit.net/openbookings/
http://bumblebeeman.sourceforge.net/
http://rapla.sourceforge.net/