Hello,
Unfortunately that's a major challenge for robotic arms, there are hardly any standard tools, usually you need to build at least an adapter plate to e.g. mount a gripper to the robot. UR had a pretty good idea with their UR+ platform (
https://www.universal-robots.com/plus/products/?) however even that does not contain prices.
That's one of the reasons why robot integrators make good money, as they offer a package price and deal with all the details. Of courses that's quite a bit more expensive than doing it by yourself.
Regarding the spindle: Usually you need the spindle and a fitting inverter. The opening/closing/cleaning... of the spindle is done via pressured air, so you need digital outputs at the robot and connect them to valves. Often, the spindle also needs a 24V power supply, e.g. for the fan or for operating certain buttons. And a lot of cables!
That should give you an idea, the complexity of the integration of the spindle depends mostly on the chosen inverter, many of them are a huge pain to program. Especially with a spindle I would recommend to get one without too many fancy functions that you don't need but make the handling more complex.
We're currently using an HiTeco spindle, I've also seen plenty of HSD spindles. For robots, they usually recommend the long-nose variants.
Hope that helps a bit with estimating the effort of integrating a spindle!
Best,
Johannes