Paint is one of the cheapest ways to change the look of a room or a piece of furniture. Mis-tints are sold cheap(50% off or more) at most stores that sell paint, you just have to keep looking till you find a colour you like. Don't buy a brand of new cheap paint, it's more headache than it's worth. Buy a decent brush and look after it, it will last for years. If you have a Habitat for Humanity Restore where you live, they have cheap paint too.
Learn to sew. Old sewing machines work fine and if you look around you should be able to find one in good working order for less than $100, who knows, maybe almost free. Try to get one that still has the manual with it. Sewing may be one of the cheapest and most rewarding hobbies there is--you find a nice piece of fabric, old clothing or whatever, and with a little of your time and some thread(buy the good stuff, the cheap stuff is a waste of money) you can turn it into curtains, a cushion cover, a wall hanging, a slipcover for a chair. Some of my favourite shirts are cut down from men's ones from thrift stores--great fabric, but they were really big. If you have any fabric stores where you live, the big ones almost always have a bargain section and you can find some really good deals there.
Go to garage sales, the season is starting. If you have a car or can round up a friend with one, go to all of them.They can be a great place to find knick-knacks or just about anything else for a house. You get best choice when you go early but the best deals when you go near the end when people really want to get rid of the stuff. Pick a colour or style theme and stick to it so you don't buy stuff just because it's cheap, and try to buy quality when you get furniture. If it's beat up but sound it can be refinished and that takes mostly your labour.