This is an interesting point and one which can be argued back and fourth.

The truth about the situation.
You are lucky to have DJ work.
Don't sit on your laurels as there are countless others who will do your job for less/free.

I can see what you mean about selling yourself cheaper not being a good idea and how this can go against the grain. (It would for me too).

Something that would help your case would be if you could get people in earlier. And I think that may be what the bar wants you to do. If people are coming to hear you play a afterwork chillout set then they can't not pay you because you are fullfilling your job as a DJ by drawing in the crowds.
Make yourself more viable as a DJ by having initiatives and generating a good atmosphere for whatever time in the evening it is. As the evening goes on spice it up but start soft.

Having two nights a week at the same place means that you are doing something right. So keep it going, but don't be afraid to work even harder and promote the 'early evening chill' too.

The night is what you make it so this is your chance to prove to the owners that you are worth the money.

A lot of bars and stuff I have worked for have given me a percentage of the total takings so if I didn't get people in, I didn't get paid... simple.
Promote yourself shamelessly.

Cheers
Nem

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https://www.mixcloud.com/Calvin_Karass/