Hi @Katie_baasecamp 👋 some subscription apps allow for the first month to have a different pricing but setting it up as separate items varies in app support and has to be researched.
If the store is on shopify-Plus see shopify-functions capable apps using the cart-transformation feature.
Online-sales channel only, for the non-subscriptions services, or all 3 service types without an app, the registration-fee could literally just be a product that gets automatically added at the cart step on the online store website.
For vintage themes only see the advanced gift-wrapping customization
If you need this customization such as for an OS2.0 theme then contact me by my email for services.
Contact info in forum signature.
ALWAYS please provide context, examples: store url, theme name, post url(s) , or any further detail in ALL correspondence.
Good Hunting.