Savannah here from the Shopify Guru Team.
When it comes to taking a deposit, there are a couple of workarounds that you can employ to get the job done.
One option would be to use a partial payment app like LAY-BUY to create a short term payment plan (your desired deposit plus the rest later on).
You could also list your products at the deposit price, and note that the remainder of the payment would need to be paid as the services are delivered. If you haven't already taken a look, I'd recommend checking out an event booking app like BookThat which will allow your customers to reserve your services.
Don't hesitate to let me know if you have any further questions or if I can clarify anything!