Write Function in Google Sheets
Cost varies on the challenge of the function. But, I can either educate you on how to write a custom function in google sheets/use their scripts to access an API. Or, I can write it for you.
Training & Qualifications
I have written several scripts for the startup that I work at to enable others to access the API's of vendors that we use. That basically means that I'm not the fastest coder or super-pro but I know my way around google sheets scripts and functions.
Availability & Preferences