I can help you to migrate from your existing Universal Analytics tracking to Google Analytics 4.
What:
1) We discuss the project details and agree on the pricing model(hourly/fixed) and/or the price.
2) We create a Measurement Plan - document, that describes, what dimensions and metrics we need to have in GA4 setup. What events to track, what parameters to send, etc.
3) Implementation: GA4/GTM interface configuration, writing instructions for your developers(if needed), development.
4) Collecting the real data and testing. Fixing issues, if needed.
The final price is very different and depends on your website, business goals and many other things.
But I will do my best to deliver the setup, which will efficiently work next 3-5 years. Or even more.