I've been very happy with MarkMonitor. They have good customer service, a good reputation, and best of all, they auto-renew domains and send an invoice. That means that the failure mode is "domain is renewed, I owe them a check."
If your domains are riding on a credit card, you potentially have a failure mode of "card was declined, my domain did not renew, everything is down."
My invoices say $20/yr per .com; other TLDs are more expensive. Because we have a ton of domains we spend over $20k a year with them. I'm sure there is a minimum but I don't know what it is these days.
I would not say MarkMonitor is a tool for startups. It's a tool for organizations that would lose a lot if they lost a domain. I bet Zoho wishes they could go back in time and spend $10k to avoid this problem they had.
If your domains are riding on a credit card, you potentially have a failure mode of "card was declined, my domain did not renew, everything is down."