I'll bite on this one as I have a similar problem. I live in a city and don't need to drive.
I took my db down to the studio to record in the hardcase with wheels on the base. It was a giant pain in the butt, it killed me BUT it was only a 5 minute walk. On the way back I put the whole thing on my back which worked and was easier, but I expected a swarm of children to follow behind me wondering where the circus was! The hardcase must weigh 5-6 times what the db does.
I'm starting to busk this xmas season with two old friends, guitar and violin. It will be around the city so I don't have to move it far. I'm looking for a soft case for that. Something designed to go on my back. I've seen cases that are designed to be as small as possible with the endpin sticking out of a hole in the bottom and the straps holding the instrument pretty high and stable.
Anyone have any recommendations? I've seen great looking ones come up here and there on ebay for fairly cheap. I'm into ordering from the states or somewhere eastern basically because the same case that costs $250 in the states works out almost $500 plus shipping here in the UK for some insane reason. Something with the features I describe, fairly light, strong straps designed to be carried on the back, for 3/4 size and around £100 ($200) would be ideal.
On a lighter note while in Poland one group busking on the street had a lady in her late 60's playing the double bass, when they were finished the accordian player hung it from his neck via a leather strap from endpin to a bolt on the back of the neck then picked up a chair, his accordian in a hardcase and another box with props in, he was about 4-5 feet tall and looked to be in his 70's!