Tennis began as a sport for the upper classes, and its evolution into a sport for every income level is still far from complete. If you don't have a lot of money to throw into tennis racquets, court time, and lessons, don't let that stop you from playing. With a little creative effort, you can cut the cost of playing tennis dramatically.
A racquet is the single most expensive piece of equipment most tennis players buy. High-end graphite and titanium racquets go for as much as $300. At the other end of the spectrum are aluminum racquets that start at around $10.
With graphite and titanium, you're basically paying for lightness and rigidity, but the advent of wide-body design has enabled aluminum racquets to be much more rigid than they used to be. For beginning players, flexibility is not important. Flexibility causes inaccuracy when the ball is hit hard, but beginners don't hit very hard or accurately. Advanced players need a frame that won't distort upon impact with the ball, so they almost always opt for graphite or titanium. Could an advanced player be happy with an aluminum racquet? Unlikely, but not impossible, if he or she did not mind a beam wide enough (in the side profile) to provide sufficient rigidity.
If you're just getting started with tennis, you'll be happy with a $10-$20 aluminum racquet with a fairly wide beam. If you're an advanced player on a budget, look for closeouts and demos of graphite racquets. I've seen discontinued models of top-notch graphite racquets on closeout for as little as $60. Check the online retailers for bargains. Your local pro shop probably sells demos, too. These slightly used racquets usually sell for around half price. The auction sites are also worth a look. They typically have lots of racquets for sale, some of which are brand new.
Keep in mind that a racquet will last for many years. It can be a substantial purchase, but if you take good care of it, its cost per year will end up pretty small.