Yes I'm happy to build it, unless it makes more sense for stockers to post the rectifier to Arthur Aardvark and minimise the journeys the bits have to make? Arthur, are you up for building it as you have the box? No problem if you'd rather I do it.
So.... playmofire let's be clear on the requirements:
1) This has got to operate just the one signal? Do you foresee getting any more signals you'd want to operate (ie. would you ever want more switches and output wires adding to the box?)
2) You'd like a small box with the dpdt switch on the top, the rectifier etc. inside
3) The box will need a pair of wires in and another pair out. Do these need to be long or short? Will the box be close to the Playmobil supply? I'm thinking maybe just a few inches of wire each side (or out of the "back", whichever way suits you best), and you can connect with "chocolate block" terminals? Alternatively I guess could fit some sort of simple plug/socket arrangement?
4) Is it for indoor or outdoors (ie. does it need to be weather-proof at all?)
Let us know exactly what you need made up?
I wouldn't worry about the money side of things just yet.