27 API calls => 27 UI blocks to show that data.
I am guessing, you also do not have a Site in place and looking to build that.
If you have a design in mind, that would be awesome. If not, we can discuss and come up with one.
Since it is an Application, rather than just a Plain Website, I would suggest using a Framework on the lines of Angular, because it takes care of a lot of things. ( you can go with React Or Vue... Just that I am proficient in Angular )
PHP is a good scripting language, but so is Python Or Node. Is there a specific reason to side with PHP, or is it just like that? If there is no good reason, I would also suggest you use Node / Python ( Better Performance )
Development Timeline
27 UI Blocks - a minimum of 8 hrs each - 27 Working Days
27 APIs - a minimum of 2-4 hrs to code - 14 Working days
Add Websockets Or a Platform for showing real-time Data - 5 Working days
Keep a Week extra for the integrations and testing - 5 Working days
Total - 51 Working Days for a Single Developer.
50 ( rounding off to 50 ) * 8 = 400 hrs of work, at $12 an hour, would be $4800.
Ohh, but that is if you do have a design and how your Website looks and feels. If there are no such specs in place, that would be extra -
5 days worth - at $20/hr = $800 more. [ 5 * 8 * 20 ]
All in all $5600. ~ $5500.
Anything, else below this, the quality would suffer. [ The timeline can be brought down with more developers - but the price would be the same. ]