I can drop roughly 40-60 for 2 4gb cards at 1866 mhz. So mostly likely $120 max to make thd upgrade. And yeah I know 800 mhz is slow asf. Thats why im upgrading.
Used I can easily pick the upgrade for $70-$80. New I can get it for about $120 maybe $100 if I look hard enough
I would be doubtful about finding that price new for the RAM.
Keep in mind by the way, you need to replace all 4 sticks. If you put 2 more in at 1866, they will downclock themselves to match the incredibly low frequency RAM you already have.