Notice:
The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.
Beyond the cost of the porta-potti (Get a 5 gallon one) you just need some hose, clamps, and the deck fitting. The deck fitting is the most costly item. I recommend you buy the best hoses and fittings that you can. I would guess you will spend about $150 assuming about $100 for the deck fitting. There are deck plates for less which would reduce your cost.
I made the conversion several years ago, I'll see if I can find my list and some receipts. Wasn't a difficult install, toughest part was the holding tank and it's platform.
Not sure what boat you have, but if it's a C250 with wheel, be careful with placement and sizing of the holding tank. A previous owner of my boat had to downsize the holding tank to 6 gallons because the steering mechanism was rubbing against the holding tank.
Some choices exist for the installation. A Todd 13 gal holding tank can be installed directly aft of the wet locker or use the factory location in the aft compartment and use whatever tank they fit there.
Just aft of the wet locker offers shorter runs of piping and some of it can be standard sch 40 pvc.
Notice: The advice given on this site is based upon individual or quoted experience, yours may differ. The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.