I think the 'quickest' way you'll get a connection is to go dial up. That way you'll at least be online albeit slowly!
Getting high speed Internet 'quickly' isn't really possible - you have to wait for the install etc etc, adding the complexity you only want it to be temporary, makes it even more difficult!
In situations like this, you either go without, or stump up the cash to get what you want. A solution would be to get a 3G or HSDPA datacard off ebay or if thats not possible, buy one from Vodafone or T mobile, get on a pay as you go tariff and stump up the costs of being data connected whilst you run the business until you settle somewhere more permanent with a landline internet connection. I think you'd find it quite difficult to find someone willing to 'sell' the remaining part of their contract, although I have seen some adverts on places like Gumtree.com so try there.
Go to adslguide.org, look at their 'wireless broadband ISP' providers too, around my area we do have wireless boradband internet, I tried them 2 times on a month's free trial - but didn't really like it as it was only 1MB. i think they did want a 12 month contract, but if there is a provider in your area, take the month's freeby trial and then give it back!
There are trials of WiMAX in certain areas of the country, have a look at those, not sure how you'd get on them though.
I can't think of anything else -
good luck!
DtM! West London UK!