A LOT more than two
The cheapest--and the identical replacement for the OEM installed toilet--is the Jabsco manual. Next up the "food chain" of quality, durability, and reliability is a tie between the Wilcox-Crittenden Headmate and the Groco HF (the Groco MIGHT be a little better quality, but tends to be the most temperamental when the pump seals become worn). At the top of the part of this food chain that's appropriate for your boat are the Raritan PH II and the Raritan Cricket...rated #1 and #2 by Practical Sailor and just about everyone else in the industry as the best manual toilets under $500. Everything after that IS over $500...up to more than $1,000...and overkill for your boat.Installation is the same for all of 'em. The mounting bolt hole patterns are unlikely to match your existing holes, but that's not a big deal.West Marine is prob'ly the most expensive source for any of 'em. Check Defender Industries and BOAT/US before buying. You can check out the specs for all of 'em in more detail on the mfrs' websites:www.jabsco.comwww.wilcox-crittenden.comwww.groco.comwww.raritaneng.comYou might also want to read the articles in the Head Mistress forum reference library (LIBRARY, not archive...link is on the HM forum homepage) for information about proper installation, operation and maintenance for your entire sanitation system.