These cost $150. A cheap DIY minisplit is over $1000 (double that if you get one that doesn't need a vacuum). I'd love to have the minisplit HVAC in my shed, but cost drives me away.
Sure, yeah, double it if you want the pre-charged lines. But I found that installing the lines that required a vacuum to be easier than using the precharged lines (as you don't need to be as careful with the lines before you release the charge into them).
Regardless though the minisplit (or central A/C) isn't a good substitute for a dedicated dehumidifier. You're not going to get the RH very low.