Here's what I did...
My first step into becoming a network admin was to learn about networks. More specifically, SOHO and Enterprise networks. Most of my skills were aquired by figuring things out on my own... but here are somethings to get you started:
CCNA - Cisco Certified Networking Associate - This certification is the entry level certification for Cisco Systems and a good way to begin a networking career. After finishing the 4 module course, you will have the basic skills required to manage and deploy a good network. Most people who obtain this certificate start out as Network Support Specialist and can earn anywhere from $40,000 - $70,000 depending on your skills and the company.
Most CCNA's continue their studies to earn their CCNP, CCDA, CCDP, and even the CCIE, to further their knowledge and bank account.
CNE - Certified Novel Engineer - Although you will learn about Novell and how to use it if you take the CCNA courses, it's not a bad idea to get the certification
MCSE - Microsoft Certified Systems Engineer - A real good certification to get if you are working with Windows Server networks.
As for costs, those courses can cost quite a bit. Fortunate for me, I took mine in High School for free!