Is there an appropriate spot on here to advertise a latex-related job/commission? Alternatively, would it be appropriate to privately message some users and invite them to apply for a job/commission? Or would this be generally frowned upon as being not what this site is intended for?
I just signed up for freelancer.ca (see edit below for more details) and basically you can look for freelancers in specific areas to do your "projects", including LaTeX. From what I can see, some of the freelancers seem to have really solid reviews and even have examples of their work. You can also post your "project" and have freelancers bid on it (but stick with the LaTeX tag only; otherwise, you'll end up with a LOT of bids from freelancers who know nothing about it).
As an alternative to this, it really would be nice to have somewhere on here as a "LaTeX-for-hire" job listing forum. The TUG jobboard seems to be pretty dead (no new jobs since July 2014), and their consultant listing seems to be mainly geared towards heavy/intense/professional jobs.
As far as I can see, the freelancer website seems to be the best place for getting smaller jobs done (although they can do big ones as well, but I would rather have bigger jobs done by a professional with their own website or an owner of a prominent LaTeX package, etc). There really should be an SE alternative to this for smaller jobs (not for huge ones) IMO, or at least a LaTeX-specific one.
Edit: I just finished a project I assigned to someone I hired on there, and he did a pretty good job! There was a lot of back-and-forth communication to make sure the TikZ pictures (in my case) came out the way I wanted them to, but the person I hired at least (can't speak for others) worked pretty hard to make sure I was satisfied. There are some PhD students on there, but I just hired a physics grad student.
Also, you don't pay for the entire project at once, you actually just give a small deposit fee first, and don't pay them more until they give you deliverables/updates half way (you can customise this to set more milestones than just halfway too). This is a good thing since you don't have to worry as much about money going to waste. Of course, as Johannes said, with freelancers you never know what you'll get, but I think this system helps minimise the risks of that (with the payment structure I mentioned).
Note that this is just my experience, but I think if you choose a freelancer wisely you can end up with similar results. I should also say I don't work for the website or anything like that, I was just desperate to get some drawings done for a (overdue) paper and that's why I used them.