Signwriting doesn't have to be expensive. Got a basic vinyl, just text in single colour done off of ebay, two sides and back for only 30 squid!
Back to the question though, when you say you have no time ... not even a one or two hours? As this is all you really need, either to just post flyers or best of all go door knocking. I was seriously thinking of going down the route you are thinking when my brother was about to join me, but we decided just to spend a couple of hours a day canvassing. We only did probably a total of 12-14 hours canvassing, and got 2 full days work for both of us, with work still coming in from letters we posted to those we couldn't speak to.
I will hasten to add as well, that we canvassed in the middle of the day which is not the best recommendation, I'd say between 4-7.30 at the latest is the best time, esp this time of year while it is still light.
So, the short answer is 'No' !