TLD stands for Top Level Domain. So are .net and .org. There are many TLD's issued by entities all over the world. If you are on the internet to do business or e-commerce, I recommend you start with a dot com. Depending on the size and nature of your business you will then need to look at getting your domain name in other TLD's to protect against others trying to steal your potential visitors and possibly damaging your reputation.
Sophisticated buyers use the newer, better services and pay substantially less.
I suggest you look at the banner at the botton of this page. Other TLD's have their own fee schedule, with most other U.S. and foreign TLD's costing more. Depending on which service you use to enter your registration you may or may not be charged a service fee in addition. Make sure you know what fees are attached, and what extra services, if any, are included. A domain name broker is just like a real estate broker, only they sell domain names.