not that bad of a price..althought you can get a thermostat for about $5-10 and a water pump for less than half what theyre charging..
i know i can get a $35 water pump and $5 thermo for my wrangler...
they definitely over charging you some (it's what shops need to do..) but at least your not getting robbed..but if you cant do it yourself or know someone who will do it for cheap, their price isnt the worst
like CS_films said i dont know how long it takes to replace/flush on the gmc savanna but here are the prices for some parts..theres always a mark up when you buy parts through the shop (usually 110%)
i also have no idea what year/engine your savanna has