amazing question. Relevant to me right as I look for a developer myself.

There are not a lot of people looking for app developers, so ads would have been the last thing I would have suggested.

An easily scalable business model is to hire local sales contractors to find and funnel leads themselves in exchange of sales commission. They become 1099 and you only pay if they sale. You can create a site or squeeze page that reflects their local market but besides that your marketing costs will drop significantly while sales should increase that much more, as I often find their results directly proportional.

Best of luck!
Humberto Valle
#UnthinkStrategy