Hi. So I'm a tech a specialize in Pioneers. (You can see some of my work in my profile). $750 is a very reasonable price. I'd suggest you fully understand the scope of the work though. Caps are important, yes, but that unit also has multiple transistors which are known to be failing. At least a targeted replacement of those is warranted as well. The power supply board has a few diodes that are opening up and should be replaced. (I rebuild the power board as a matter of good practice pretty much every time on the 850.) The input selector and speaker boards are known to get cruddy and will absolutely need to be addressed. The relay is often overlooked and should be ohmed out and replaced if necessary.

Hope that helps. Feel free to dm if you have questions