Ask HN: Launching side project in 2wks with $4k mktg budget. How do I spend it?

Pretty much what the title says - I've spent the last couple months writing a career advice guide for early career developers (https://www.crackingthecodingcareer.com/). I have 4k in presales thanks to early supporters from Twitter and my blog. I just set a launch date for Jun 1st and realized I might as well go for broke on this thing and just use the presales entirely on prelaunch marketing.

I've hired a friend to help me do some small design work, but I feel like I could go for something a little more ambitious with this budget. Got any ideas for how to spend my money?