Exhaust
 

I'd like to straight pipe my dads 08 dodge Cummins but I'm not sure what's all involved like can I just straight pipe it or no

Go for it- farm boy diesel has the best prices I've seen on most exhaust systems. If you are looking for loud go 5" - will likely need to keep 4" downpipe due to firewall clearance

But is anything special needed to bypass sensors or the emissions shit?

Will need the pcm tuned to turn off the sensors. Efi live, race me, h&s are a few that can do it.

What's the cost to do all of this

Probably about $1200- they sell kits on most diesel websites that include all pipes and H&S kit.

for tuning I would recommend spending the money and going with EFI live