@Gargron thanks for replying! that you're in favor of fair compensation is great!
what you can always do in this case is encourage your mods to be bold and estimate their time realistically, (for example, being on call is not exactly "free time", and so on)
sometimes, often in smaller projects, where people volunteer at first, people tend to underestimate themselves..
@distel I've always paid the mods a mutually agreed upon amount. I'm in favor of fair compensation, but it's up to them to decide how much exactly that is for the time that they put in (which is not full time).