If your budget is tight, get a slot cutting bit for your router. I would advise against getting a cheap biscuit joiner, other flaws aside, the killer is that the fence assemblies are usually woefull, and 9 times out of 10 result in non parallel slots. This then gives an uneven joint and leaves you with half an hour of hand planing to put it right.
My advice: If you can afford it, get a good one. If not, £30 buys a good Frued biscuit cutter for a router.