I personally have a number of small and medium-sized projects going at any time, and I have a few rules for how I handle the money for these projects. It's important to me that each project pay for itself along the way, or that I gather start-up funds specifically for each project. If I need start-up funds, I'll usually write a couple articles for the Yahoo! Contributor Network until I have the $10-20 sitting in my PayPal account that I need to get started.
From there, I like to have a separate spreadsheet for each project which lists the funds I've earned specifically for that project and all of the expenses I have for the project. This method of budgeting my money forces each project to have a positive balance of profit. It also helps to never feel like I'm wasting money by working on any of my projects.
Once the project is earning money on its own (because I really like the idea of passive income, no matter how small), then I can reinvest the money it makes into scaling up to make even more money over time. This way, I make a small up-front investment of time and effort by writing a few articles for the Yahoo! Contributor Network, and I get to see a return on that time investment over and over again. This really helps to keep me motivated, especially when I don't feel like budgeting money responsibly.