this calculation doesnt include the free tier which can actually cover a lot but rate limit with DOs doesnt seem to be too pricy and from my own testing DOs are normally faster than 30ms for only simple storage ops so could be cheaper too not that duration really had any effect on the price though lol
And DOs also have the advantage that it will spawn close to the user making the request whereas upstash would be single region that you select unless you use multiple dbs. Not to mention upstash limits commands per second to 1,000/sec for paygo which is a lot but
Unless you do like a endpoint /cars/* is 10 requests per second and /cars/<specific-id> can only have 1 request per second which would double the cost.