Depending on what year your cherokee is it should have spots for 5 1/4" speakers in the 2 front doors and in the rear liftgate. Are you looking to spend 4-500 for everything (i.e. head unit, replacement speakers, amp, and subs) if so then you will have to go with the lower end products which have very low reliability. If you're looking for a decent system for a fair price then I recommend Pioneer. They have moderately priced cd players, speakers, subs, and ok amps.
XJace right now I have a alpine cde9845 cd player but will be upgrading that soon to a dva9860. Dynamat is good for flat areas and cars but when you have a suv it's best to get either the dynaliner that sprays on or use the spray on truck bed liner. They provide a more uniform coating and contour ALOT easier than rolls of Dynamat. Eventually once I save up enough money I'm going to line the entire inside of the cherokee with dynamat and dynaliner, replace all weather seals, replace the 3 big back windows with plexiglass and further mods as it has the perfect space to go with big systems.