What is the best way to get a subdomain to be masked [look like] a domain?

Hi…I’m putting together a site for a real estate company and I’m not sure how to put their request together. They want their main domain to showcase their properties for sale and once a property is clicked on their main domain, that property comes up as a custom-template single-page site. I figured to use subdomains for each property but the company owner does not like the way the subdomain URL looks on their printed materials—it’s too long and company owner believe buyers obtaining the printed materials will not type in such a long URL.

For example… https://realestatecompanydomain.com as a main site. Say the company has 10 properties for sale, I figured do a www.subdomain.realestatecompanydomain.com for each of the 10 properties.

My solution was to have the company purchase 10 domains and each domain name correlate to the street name and mask each subdomain with a domain.

For example… www.subdomain.realestatecompanydomain.com—>mask with—>www.mainstreet.com

The solution above would remove the lengthy subdomain on printed materials to a more shortened and simple domain.

But my solution seems to be costly and ineffective. I’m sure there’s another way of accomplishing what they want but I cannot seem to find an answer. I’ve read about CNAME Flattening and DNS providers such as CloudFlare but I’m not well-versed at those options.

I would appreciate any help.

Thanks!