Advice on selling a lot of Lego?
Post an auction on ebay, and let the buyers determine the worth.  Include a lot of pictures of what is in the lot, so buyers know what they are getting.  If you go random, the most folks will pay is what it is worth with all low valued pieces. 

If you want to make more money, sort the Lego out, and see if you can complete sets.  For some sets the complete set will sell for more than the individual pieces, for other sets the individual pieces will sell for more. 

If you want to maximize profit do some research on sites like ebay, bricklink, brickowl and see what the parts you have are selling for.  If not, then just post it as you described it here, as an auction on eBay, and see if anyone bids.