Technically, WordPress is built in PHP. If you are choosing between having a site custom designed in PHP versus WordPress, WordPress will be much less expensive.
The main thing to understand with regards to WordPress is that it requires a lot of maintenance to keep it secure and running right.
It's open source, so when updates come out, you get the updates at the same time as the hackers. This in conjunction with the fact that it's a very popular platform, makes it a target for hackers.
Personally, I'd recommend you add a 3rd candidate into your mix of options. That would be some kind of a hosted solution. Just do a google search for, "Hosted Real Estate Agent Site" or "Hosted Property Management Site."
These will usually be much less expensive as far as initial cost goes, however, the monthly upkeep can seem a bit high. That said, maintaining WordPress can cost $50-100/mo, when done properly.
Hope that helps.
Website Developer with two decades of experience
I would suggest that you should go with wordpress rathen than PHP because in wordpress your more than 70% works can be done by just simply installing various plugins and you can get brand new websites within just few minutes with minimal code.
On tha other hand, if you choose to develop a website in PHP then you have to manually write thousands lines of code which is nothing but a waste of time and energy.