Paper plates will cost as little as $3 to $4 at the grocery store for 20 or 30 plates. Even better deals can be found on the Internet. For example, some online retailers sell 1,000 paper plates for $30 (shipping and handling included).

Depending on whether you prefer standard dishes or fine china (and assuming that you do not already own either), you can purchase a new set of dinner plates for as little as $10. You can pay more for better quality or additional quantity.

The dishwasher is the "x factor" in the equation. Every time you run a dishwasher, you are using water. If you are charged monthly for water use (as are most apartments and households), then you need to factor in the water use, which will vary depending on your local rates.

If you have a family of four, and you invest in 1,000 plates, the plates would last you approximately 250 meals. If you eat three meals a day, this would equal about 83 days, or almost three full months.

Say you purchase an average set of plates for $25. The one-time cost is already cheaper than 1,000 disposable plates. Now you need to factor in your local water rates and estimated use.

Investing in standard dishes makes more financial sense unless your local water rates are extremely high and you plan to use the dishwasher once or twice per day. Paper plates, however, are also much easier to clean (since you just throw them away). Thus, paper plates also save time—a benefit for some people. Still, in the most simple economic sense, it's cheaper to wash dishes.