Congratulations on your achievement. $500K ARR certainly doesn’t make you too large to sell. The valuation you can expect will depend on your current growth rate, gross margin, LTV:CAC etc.

https://burklandassociates.com/2023/03/21/selling-your-startup-external-preparations/
https://burklandassociates.com/2023/03/21/selling-your-startup-internal-preparations/

We did an analysis of this a couple of years ago. At that time, we found that from the business side, monthly SaaS contracts need to incorporate a premium greater than 22% to achieve the same economics as an annual SaaS contract, after factoring for churn, etc.

https://burklandassociates.com/2021/09/28/monthly-saas-contracts-vs-annual/