Decide what you want to learn, and then buy some hardware.

You can do a lot of things in labs, virtual environments, and online, and if you prefer that, that's fine. This wiki is dedicated to hands on learning and immersion. Like I mentioned in How Did It All Begin? I fully believe this approach is much faster, more effective, and more addictive. Investing in yourself and your development is money well-spent, because it can potentially mean you making more money, with the side benefit of gaining enterprise grade performance at home.

If you're aiming for CCNA/CCNP, there are prebuilt labs on ebay, usually averaging $300. What's great about these are, if your overall goal is to get certified, and you don't intend to practically use the devices, you can put them right back up on ebay for the same amount if you get certified quickly enough. However, again, my suggestion would be to actually use one of the routers as your edge device, and connect your home devices to the switches, and really get dirty. Once you learn enough, you could even segregate your home from the lab and learn how to keep that traffic isolated, while still being able to get into it to play around.

For virtualization (hyper-v, prox mox, esxi, etc), a generation or two older HP Proliants are a great. These can also be found on ebay for roughly $250 depending on the configuration (usually 800gb of SAS over 4 drives, dual xeon processors, and 48gb of ECC RAM). This is more than enough to run tons of VMs and you can always throw more storage or RAM in them later.

If all this seems like it's way more than you can handle, start with a simple layer 3 switch. If you want to make use of it practically in the home as well as for a lab, go for gigabit ports and PoE if you intend to power anything. You can typically find these for roughly $100 on ebay.

Into wireless? Cisco WLCs can be virtualized with an ISO, they don't require much computing power, and typically use 2-4gb of RAM. An old pc or laptop would be perfect for this, or, purchase a server and throw it in a VM. Older generation APs can be grabbed for cheap on ebay, and if you don't want to invest in a switch, they can be powered via ac/dc power adapters.

Are you a reddit user? Check out /r/homelabsales for deals on equipment from other homelabbers like yourself.

Ebay junkie? Save My Server is a great store for Proliants, Power Edges, and other great gear.