High quality (expensive) scissors usually have a screw that can be adjusted as required, cheap scissors are held together by a rivet. The rivet can be tightened by placing one side on a anvil (any lump of steel works) and hitting the other side with a hammer. Do NOT overdo it, unlike the screw there's no easy way to back off again if you go too tight.
Dull blades will suprisingly still cut fairly well if the tension is very high - force the blades together against each other hard enough and anything put between them
will be sheared off, but you will need to use much force to cut with it. When the blades are sharp you need very little tension to get a perfect cut. You might need more practice finding the correct tension than sharpening the blades - scissors with screw lets you experiment until you're happy, the riveted ones, not so much.
Well, there's diffrent kinds of wasting money. If you buy old quality scissors and bring them back to working as well as when they were new you've both got some practice and a great pair of fully functional scissors. You can use them yourself (once you've got used to sharp high quality scissors you don't want to be without them, just like any other good tools) or you could sell them. I'm not sure about the prices in your area, but I've picked up a few old and abused 8-10" dressmakers scissors for equal to ~2-3$US, now that they're back in working order I could probably sell them for ten times that. Ofcourse, after using them I like them way too much to ever let them go...