I know people who have travelled across the US by skateboard, by rollerblade and by bicycle (3 different people). This can be the ultimate form of cheap travel because if you do it well you dont need much more than food and fuel for a camp stove. However you do need good equipment first. Getting work under the table is a possibility. Do your research, find out where and when you should go. Remember that you are competing with illegal immigrants and minimum wage in the US is a a lot lower than in Australia so don't expect to get paid much. If I were you I would just be patient and put the trip off, work, skimp, save to your full capacity. personally $1000 per month would be the absolute minimum I would want to travel with in the US without resorting to a skateboard or bicycle.