Two excellent choices, John:
(And btw...I'm no longer connected with Raritan, so I no longer have any axe to grind by recommending their equipment) The Raritan PH II has long been considered the best manual marine toilet in its price range (under $500). And despite Sam Lust's negative experience installing it, I really like the Raritan Cricket...because, instead of the usual piston/cylinder pump beside the bowl, it has a diaphragm pump directly below the bowl...which means no moving parts to wear and need frequent replacement of seals and o-rings. In fact, the "repair kit" includes the entire pump assembly except the housing...that's how infrequently you have to "rebuild" it. Change the joker valve every year and that's just about it. It fits in the same space as a "compact" model, but is available with both the small "standard" bowl OR the larger "highboy" bowl. And, the pump is designed to bring in less flushwater than the amount of material it pushes through the discharge...so your holding tank doesn't fill up as fast. Both toilets are around $200-250 at any of the discounters...a bit more than the "disposable" toilets, but a LOT more bang for the buck IMHO. Plus, as even Sam noted, Raritan's customer service is outstanding...the best in the industry. Alternatively, the Wilcox "Headmate" has allegedly improved tremendously under new ownership who brought all the mfr'g back to the US from Costa Rica and replaced all the worn out tooling...so if your budget is REALLY tight, it might be worth a try...I haven't seen or heard of enough experience to recommend it OR warn against it.