You dont need expensive 3rd party controller cards. If you are going with software raid, even cheap sata controllers do work in the sense that if a drive is tied down it only ties down that particular controller.
However with these cheap controller cards, anything hardware based will really be terrible in performance. They are ok for hard drives addressed via software without using the controller, so if you are using windows, use windows generic drivers, dont go installing drivers for it. On linux it'd auto detect it or allow you to set it up but again, linux relies more on software, and as long as you are not using it for any hardware related task, you will be safe as long as the OS directly accesses the drives and not let the controller be the middleman.
On expensive raid controllers they can be worth their money. Some of them have DRAM slots or onboard ram allowing for cache features that can speed things up, and features that can really help, however they are restricted in hardware mode to either that card only, or cards of particular makes when using raid across controllers. They can also really take the load off the OS too especially on windows.
If your motherboard has SAS, all you need is a SAS to sata cable, because the SAS will have plenty of channels, there will be no controller needed unless you are going for SAS cards.