What do you use to create automated email workflows?

I'm looking for a cost-effective tool to add email automation to my new product.

Ideally, I would like to:

• Start email sequences based on events (e.g. welcome email 24h after a user joins, feedback email after the user performs a specific action)
• Add users automatically using a webhooks/API calls

I have looked at the following tools:

• Customer io: I have used it at a previous job, but it is quite expensive for an indie project ($100/month).
• Drip: It seems nice, but the cheapest plan is still pricey ($39/month).
• MailerLite: I have tried it. It's cost effective, but they only show monthly stats and it does not seem easy to trigger a workflow based on an event.

What do you use?