My 2004 altima is consuming oil at an excessive rate, there are no visible leaks on pavement. When I took it to the dealer they told me it would take a few days to find where the leak is and cost $250. I forgot what he said it could be leaking from but he said if it's from one area it could cost around $850 and if it was another spot it could be around $3000. I've just been putting oil in it but I know it has to be fixed is this price too high? Because I feel like I'm being taken for a ride!

Hello! Sounds like a ride to me...Since you do not see any oil on the pavement, and it's using oil at an excessive rate, I would believe you would see blue or black smoke coming out of the tail pipe...
let me know if you do...Also, does the engine run normally?...No hesitation,or rough idle?...A plugged Positive Crankcase Ventilation (PCV) valve will cause an engine to consume oil...See photos below...
First is for a 2.5L and second a 3.5L...Both cost around $10...Guru.....saailer

AIRTEX / WELLS Part # 6P1247


AIRTEX / WELLS Part # 6P1238

I’m happy to help further over the phone at https://www.6ya.com/expert/david_6df67de3b14de867

You can have a brand new engine put in for $3000 with a warranty. He may be saying the seal are bad and that's where your oil is leaking from. The $250 fee to just find the leak is excessive, $850 don't sound bad if it's an actual problem and depending on the problem if it's dealing with replacing the timing belt and other components. But I would stay away from the $3000 deal. You need to get a print out on what he is needing to charge and what parts are being used and do your research on those parts. Some will pay a $100 for a part and kick the price up to $125-$150 so be careful and check around.