2003 and 2004 are the best years for common rail cummins. stay away from 98.5 to 2002 cummins.
$14k is a bit high... prices have really cratered for big diesels. I've seen 2004 cummins go for under $10k on craigslist.
I've got a 97 12v... which is the best year for 12v. it's value has dropped in half. doesn't really matter as there's no way I'm selling.
manual tranny is preferred, but auto tranny in dodge are not as bad as folks make them out to be. for normal duties... dodge tranny will do fine... it's when you get to pulling 20k+ lbs all the time and/or boost your HP to 450+ . then no stock tranny will hold.
stock dodge torque converters slip all the time... you'd pick up 2-3 mpg in town vs manual tranny. if you have a choice go stick.
that said... my 97 12 w/auto routinely yanks 20k+lb loads with no sweat. dead reliable... would not hesitate to jump in my 97 12v and drive to Alaska and back.
I'll argue the 03-04 are the best,they are known for dropping valves,and valve seat failure.I have heard of a many failures,and then seen one myself when I built a DTT trans for a friends 03 3500,and it dropped a valve a yr later,destroyed the engine, i think it was #3 cylinder,it took Chrysler 13 days to even approve it for warranty,they fought it because he had an exhaust brake,and another 3 weeks to do the job.2 months later the replacement engines freeze out plug fell out at 60 mph on the interstate and overheated the new engine w 0nly 1500 miles on it.
The 04.5 325hp has a much better head,with better valves and seats.Although it doesnt get the fuel mileage of the early 04 and 03's.
There's nothing wrong with the 98.5-02's at this point,when they were new,Vp44 failures,and some #53 blocks,but all the bad vp44s have failed already,and the bad blocks have cracked,and been dealth with.My 2000 has never let me down,original Vp44 w 140+K on it,and 75K of that at 500+RWHP.I made 663rwhp in june of 03 on spray,and 603hp to the ground back in June of 04 with diesel only,at thunder in Muncie.Back then that was a lot of power.I built transmissions for many of my friends most of these trucks are 98.5-02s,they are good trucks,and a great used truck value now.biggest downside IMO is the fact that the quad cab is small,not much room in the truck.My 96 club cabs interior had a lot more room in it than my 2000 quad cab.
As for stock Dodge TC slipping all the time,that isnt true at all.starting in 94,they all have lock up TCs,and they lock above 30mph with OD off,or 45 mp with OD on.Once they lock,they are locked solid,and combined with the autos steeper .69 OD ratio,they will match a 6 speed trucks highway MPG because the engine is revving 150rpm lower than a manual trans truck at the same speed.This offsets the transmissions front pump,and ATF fluid friction which robs a few hp to run. In the city,and hills,the manual will get better mpg everytime,unless you get a built trans with a good convertor,my DTT torque convertor stalls about 600 rpm lower than stock,and it doesnt slip,it just pulls when you mash it,the stock torque convertor is built for the V10 gasser,thats why it feels like its slipping,its stall speed is way to high for a Cummins.A good torque convertor totally changes the way an auto drives,if anyoen wants i can post a link to a video of my truck pushing a 10ft blade full of wet snow,just off idle,with a DTT modded automatic I built.The amount of snow the properly set up Dodge Cummins will push is amazing.Throwing 4000 at a Dodge auto is well worth it if you plan it use the truck and the stock trans is worn out or in need of rebuilding.
