There are lots of things that you can do that don't cost money. Do you have a FB or LI business page? 

Ask your best clients if they will write a recommendation. Run some promotion - what is your business - Are you an authority in what you do? 

You could have zoom classes helping others ... You could even start a mastermind referral group where everyone in the group, using word-of-mouth marketing,  to help each other and refer each other (as long as your group is non-competitive)..

I'd be happy to give you an hour free on a zoom call to brainstorm things you can do. I would also be happy to connect with you.