Are you just doing mixing/mastering? Not doing any tracking?
If you are just doing mixing/mastering then you are at a huge disadvantage. The reality is that mixing you are at the mercy of your tracking engineer anyway. And I have never met a good tracking engineer that wasn't at least a decent mixer. Nor have I ever met a good tracking engineer that ONLY tracked.
So immediately you are already competing with the incumbent engineer. And in the small time/starting out most bands don't even know the process nor understand it. They want to go to the studio and leave in hand (eventually) with a product.
Pretty much the only time you deal with bands willing to separate it out is when they are very knowledgeable or working with a label/producer. And even then, in this business, reputation and who you know is everything. So they will go with someone who has a solid track record and has a sound they like.
In small time bands, my experience is that the only time they look for another mixing engineer is when they are unhappy with their current guy (including a guy in the band). Usually due to poor sonics or waaaay too long of timeframes (I did one that was 10 years old). So it is just some serious turd polishing, no DI's, clipping tracks, terrible equipment, mic placement, etc.
Better get involved in your local scene and get tracking. Offer to record bands, beginning to end for a little less than your competitors and work your ass off and turn it around as quick as you can. Go to local shows and listen to bands that are good and you like a lot. Many may already "have a guy" especially in the cheap range... so still an uphill battle... but you will get there.
Go to shows, go to parties, get in the phonebook (seriously... old school) make friends. Invite them over, drink beer, hang out, go to their rehearsals etc. Become the bands "guy." That gets you started.