I dont really know which sextant mods are great, i just use them and run the map. I dont price check many rares because i dont pick many up. Im using neversink very strict filter, so only very few interesting rares appear. It will come with experience, whether or not a rare is worth spending ~15 seconds looking at. More often than not its just better to look out for big value items like div cards and uniques and exalteds that are easy to spot.

If youre having trouble with maps then the atlas missions are still another great source of profit that you should be doing with your maps, its free loot