Man cave shed in progress

I'm planning a project for the 25th, with a budget of $6,200 USD. The main goal is to create a space for my man cave. One of the key decisions I'm trying to make is whether or not to go with a 12x18 concrete slab.

I'll be handling the insulation and drywall myself to save on costs, but I'm wondering if the slab is worth the investment. Any advice or insights would be greatly appreciated