I have a powerline adapter with Ethernet only connectivity. Is there a simple and inexpensive way to get a wireless signal via the adapter?
Hovsep A's answer will be preferable only in the case that you already have a wireless access point available. In the case that you do not have one, there cost of obtaining one will be same or more than buying a wifi extender, as Oron J suggested.
Does your PC have WiFi capability, either through a built-in or through a plug-in card? If the PC does not have WiFi capability, you will not be able to connect.
You can get PowerLine WiFi adaptors (sometimes described as "WiFi extenders"), available from pretty much all the companies that make WiFi adaptors. As Hovsep points out, you can also connect a wireless access point to an existing adaptor, but that is more cumbersome and, if you're buying them at the same time, more expensive.
Can You Hook a Wi-Fi Router to a Power-Line Adapter?