What minimum budget makes sense?
What makes sense is what you can sustain for a month to put the listing right and run one ad for the empty shift, with someone who replies. A figure from another venue does not make sense if nobody here takes the message.
Write to us. A quote with no commitment.

Say what you can keep for four weeks without taking it from the shopping. A high figure is chosen and it is switched off after ten days. You get the month agreed, the shift and the person who replies, with no borrowed figure.