How much IS enough in this profession? (legit question).
It varies a lot depending upon how you want to look at things and how you want them done.
For instance a "just graduated Java school" type would be very different to a big swinging dick type that can handle some of the nastiest types of code around, however even they might pale against someone with "legacy skills" -- a few years back if you knew COBOL then you would have seen jobs going for mega money as it turned out nobody has learned it in about 30 years and all of a sudden those that know it started retiring. However there was still lots of code out there which formed the lynch pin of someone's business, so much so that taking 4 months out to rewrite it was impossible and thus people got dragged out of retirement. A lesser version of this can be seen with old types of C code, typically something called K&R C (you might have seen things like C99, C11, C18 referring to various standards used, this would be the thing that happened before those arose).
It can also depend upon the industry you are in -- some of the things game coders do would get them paid twice as much if they worked for some big financial firm. However as game development is seen as an attractive field then salaries are kept down as you will always find some kid willing to do the job for less.
Similarly different countries represent different things – someone in deepest, darkest San Francisco probably will demand more than someone from India or maybe Vietnam (both of which have fairly high level computing skills in their populations).
https://www.indeed.com/q-Computer-Programmer-l-Seattle,-WA-jobs.html for Washington state (Microsoft makes their home here). Varies from $50K per year to over $100000 in that link.
For a start though then find the annual salary for the level of coder you reckon you will need. Divide by 12 for months and then add a bit; a professional salary includes holidays, sick pay, pension contributions, job assurances and so forth, doing contract work has none of those so the people get to charge a bit more to account for that. This would be more for a custom build for your internal use.
There are many other models though. If someone gets to remain open it changes things a lot, and it can also depend upon the size of a project. If I went to some small document writing application tomorrow and said $10000 to do mail merge as I want it and you can still release it open source then they would probably do it as said $10000 would probably represent hosting and such for the next decade. $10000 for a business is nothing a lot of the time and probably less than what it would cost to hire in some normal coders to handle it.
If you look at wordpress plugins many will have fairly nice functionality gated off behind a paywall and offers for basic work to be done or installs to be handled for a small sum.
Sometimes you get the retired coder effect, or CV builder effect where people just appreciate the perk and can do it at weekends and in the evenings.