can any recommend me a sub to go with a pair of Behringer 1C Monitors?

Hey, I need a very budget sound system set up as I'm moving abroad for a several months and taking some of my gear with me, It has to be small and not matter to much if it got stolen or broken etc. I have already got a small 100w amp which will do the job (it has no sub out). I have read that the Behringer 1C Monitor has decent mids and highs and have a great sound great for the price (£50) but everyone said you need a sub to get any decent low end. So does any have any recommendations for a small sub that will work well with these speakers for no more than £50?

Thanks