Of course I got passed over for a lot of jobs in favor of cheaper folks. But the jobs I did get were from clients who actually respected me. Also, more than once, a client who initially passed over me for someone cheaper came back a few months later and asked me to do the job after all.
So, perhaps something like that could work for you.
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Regarding the $1,200 per month limit, I'm not sure what the rules are, but perhaps you could set up a corporation that takes on the freelancing jobs and then pays you a salary of $1,200 a month? That way you wouldn't have to turn down a job for paying too much.
Maybe have the corp owned by a trust rather than you personally?
I wouldn't want you to get in trouble and lose the disability, though, so talk to somebody who actually knows what they're talking about before doing any of this stuff.