If you want to start a business on a shoe string then I would suggest starting an ironing service. I did this when I was low on funds. You start with a few notices and then word of mouth takes over. You will be amazed at who your clients are. If you want to have a look, I have done a page over at Squidoo about it. You can make a tidy sum every week. Plus it is putting you in contact with people you may never have met.
Just because you start one business doesn't mean you aren't keeping your eyes and ears open. It will keep cash flowing in while you search for a niche.
I will say this, in the financial climate, this is the perfect opportunity to start your own business. With less and less companies hiring you have nothing to lose and everything to gain.
A quote :"Failure is success if we learn from it". Malcolm S. Forbes
I would also like to say, listen to your heart. Sometimes even people who are close to you will try and hold you back.