Sliding Scale Pricing

I will be selling services and group events.  I want to set up more than one price for each service--basically sliding scale pricing.  I cannot sort out how to do this because I am very new to the Store function of Squarespace.  I have done a few searches and have not come up with details about how to do this. Any ideas or direction?   I don't think I need enough help to warrant a $400 minimum that I see for the vendors advertised via Squarespace.

Thanks in advance!