How can I market test by manually fulfilling orders?

Hi, I have a new concept for an service app. I want to test the market by offering the service and then fulfilling the orders myself manually for a very low price to see if there is a demand. What is the best way to set this up cheaply so I can target a particular group, take a small payment and fulfil the order. The target group is managers in general so need to control the targeting so as to not make it too wide at first and get flooded. Have tried offering it on Fiverr but it has been very slow so far. That does bring up some warning flags but I would like to try with a more targeted approach. I'd be grateful for any thoughts.