I pay $11 for a private L4D server for my clan. It's $17 for a public one. You pay a bit more with my host because they're a Tier 1 network, which means they're as close to the Internet backbone as you can get. This results in lower pings. If people ping fine to your servers elsewhere, that's fine too.
We keep our server private and invite only our friends on. This avoids the lobby system altogether since we connect directly with our password. It also means we're playing with friends instead of random people which makes our games far more competitive and fun.