If you are putting off buying a tablet because you can't afford to buy the necessary data plan required to surf the net, you don't need to. It appears most users are merely using wi-fi to do a majority of their surfing anyway. If you have wi-fi in your home or office, you probably won't need the connectivity in too many other places anyway.
Also you could sit at the local Starbucks and use their wi-fi signal. Also, I believe many McDonalds have free wi-fi now. In fact, a growing number of retail locations and hotels/motels have free wireless services available. So you don't need to spend the extra money on the data plan or the upgrade to make your device 3G and 4G capable.
90% of tablet computer users do a majority of there internet tasks via wi-fi. That leaves only 10% that need internet access everywhere they go. Who are these people. Probably hardcore gamers, traveling businessman, and various other folks who probably own a smartphone anyway.
Also, if you really use your pc for music, web surfing, and social networking, the tablet might make a good companion. A clear advantage o a tablet vs a desktop is the freedom to move wherever you want with the device. Lay on the couch, sit on the porch, check all your e-mails from bed, it is a lot more friendly than a desktop pc.
So if cost is holding you back, it doesn't have to be as expensive as you think. Consider the options. If you already have wi-fi and a desktop, all you really need to do is pay for the device.