Yeah but that’s deceitful unless the client is aware.
Of course they are aware. Why would you spend $55 on a theme that they might not like? Just inform them that you can cut costs down by using something premade — not to mention that it comes with support and has been tested, also with free updates from an Elite Author. It’s unlikely the client would be able to install WordPress and configure a complex theme like that on his own.
I’m sure he would take a design like that in a heartbeat over something he’s capable of making himself. Website templates, themes and other services are starting to become more common. Especially for those clients who want all the bells and whistles but don’t want to spend a huge amount of money on something coded from scratch.