Who is the best and cheapest debt management?

The best and cheapest is do it yourself. I had a debt which being paid monthly as agreed would take 18 more years. I researched credit union and got one loan there to completely pay the other debt in full, and then paid them a smaller sum weekly. The debt was clear in less than 5 years. Do your research thoroughly and you can be debt free too.

You can do it yourself with a little work. Almost all of the "debt management" companies are a rip-off, especially when you can negotiate the same way they do and not lose money paying someone else to do it. I recommend buying Dave Ramsey's book - "Total Money Makeover" - it gives you GREAT advice about how to get your finances in order, with a special section about dealing with creditors. :)

You are. With a bit of research you can learn to negotiate with collection agencies, set up a payment plan, cut your expenses and increase your income all for free