@AJ Thanks for reaching out.
During the Azure free trial period, you can create any SKU that supports the free trial subscription, and the USD 200 credit can be used to cover any additional costs beyond the free tier usage.
To estimate the costs before using API Management, you can use the Azure pricing calculator and you can refer to this pricing for more details.
If you create the Developer tier APIM then it would be a fixed cost per month as per the pricing tier along with the API operation charges as documented in pricing here.
For free account FAQ you can refer to this.
Let me know if you have any queries or concerns.
Please "Accept Answer" if the answer is helpful so that it can help others in the community.