For a standard internal painting job, here's all the tools you'll need and their costs. We've priced each tool based on the halfway point between eBay's most expensive and cheapest price.
Total estimation for preparation = $10.50
Total estimation for painting one room of 3 by 4 metres with low cost acrylic paint = $102.
Once you've bought the tools your costs decrease but your rollers and paint brushes may deteriorate over use, especially if you select cheaper versions.