There are no cheap bike racks for more than two bikes, for a very good reason. Once you get more than two bikes on the back of your vehicle, every bump in the road becomes important. You need to know your bike rack is going to keep everything securely attached, or your trip is going to suddenly be a lot shorter and significantly less entertaining. That doesn't mean there aren't occasional deals to be had on good bike racks, though. A perfect example is this bike rack for four by Thule, which is only $171.42 today.
The Thule Hitching Post Pro is a trailer hitch bike rack, meaning you can only use it on your vehicle if it has the 1 1/4- or 2-inch trailer hitch available. With this mount securely in place, you'll be able to hold four adult bikes on this rack as long as you don't exceed 35 pounds per bike, and as long as you're using a Class II or greater trailer hitch. If you're only using a Class I trailer hitch, keep it to two bikes on the rack for your safety.
The arms on this rack swivel to either compact storage mode or bike-ready mode with the aid of a locking pin. If you need to remove the arms entirely, you can do so without removing the base from the trailer hitch, thanks to a third locking pin. It's a quality, sturdy bike rack at a great discount, and could be exactly what you need for those fall adventures.