I've just successfully made my own colema board (all for less than £10 / $16) although you do need a couple of tools like a saw and drill. It would help if you could find a picture of one to base your design on, but all you need is a bucket (preferably one that's a bit see through so you can gauge the level of the liquid inside), a meathook from which to hang the bucket (alternatively you can stand on a high surface), some tubing similar to that used by plumbers or in aquariums or like the one you use for your enemas, a flat board - long enough for you to lie on with your knees up (get laminated if you can as it's easier to clean). Then you cut a hole in the board (work out from your toilet where the hole needs to be) and use something like a bucket or a bowl chopped in half to fit in around the hole to prevent output going anywhere but down the hole. You need to play around with the design here to get the bowl to fit snugly in the hole. In that bowl you need to drill a hole - this is where you feed in the tube and the colema tip. You may be able to use your enema tip provided it's not too wide, otherwise I think you should be able to order a colema tip from somewhere on the web.
Although it's not as fantastic as the real thing, it does the job.
Hope this helps!