It doesn't sound like you need something like a Frontrunner.
I had a Baja Rack on our FJ. It was built like a tank, but more than most need.
I think you could use a Yakima and be perfectly happy. Now, they aren't cheap, so you should look on
Craigslist or Facebook Marketplace. Then you might just need to get landing pads specific for your 4Runner. Actually, if you have a rack, you could use their rail grabbers.
Here's a roof rack for no oem roof rack.
https://www.facebook.com/marketplace/item/862801014114616/Now as I think about it, if you have a factory rack with crossbars, the yakima kayak racks should fit it.
I saw a set of kayak racks on Facebook for a 100 bucks.
Is Yakima as good as Frontruner or Baja? No, but it should be good enough for what you need.