I wouldn't say this one to be frugal, but then frugality varies by different parameters. What they priortize (Eg: a dedicated marketing tool vs sending marketing through app itself), what their expertise in (hosting in vps vs aws vs heroku, etc), the type of service, team size and so on. As there are 10 ways to do the same thing all with a different tradeoffs.
Being solo myself, I aim to keep my costs as low as possible as well. Until my last product, all my previous products I kept the running costs to $3 per month (just for the server on hetzner). Rest all were free services (tawk.to for CS, Zoho for email, postmark for emails, and so on). Granted they weren't making much, just couple of hundred dollars per month, but then it was pure profit and it got fun to measure the returns in profit than just revenue.
For the latest one, all in all I spend around $30 per month with close to $1250 in mrr. So it has generous spend to return ratio. The only three running cost are the helpscout (for customer support, docs, etc.), google workspace and the servers with Hetzner. HelpScout and Google workspace were my way of "splurging" the costs.
Last I checked I was using close to 16 services (ranging from marketing to revenue tracking), so weren't really skimping on tools to save costs either.
The free tools (including several the op mentioned) are awesome to get started, but many of these services' costs would jump multi-fold even if you add one other team member or go just above the limit. That's anyway all these services' business model as well.