Update: Nice discussion at Navy Matters:
The PHMs were envisioned to be minimally manned and include a mothership for maintenance and support. Manning and crew activities were to be limited to port/starboard watches. Maintenance, logistics, and support were to be provided by a converted LST acting as the mothership. We see, then, that the ships were designed to the same operational manning and maintenance concept as the LCS.Yeah, give me a couple hundred of these things and I could pose some serious issues to bad guys.
See also here.
Navy Matters puts the cost of Pegasus at about $900,000 (1975 dollars, I assume) - or about $4 million in 2015 dollars. If one LCS costs $300 million, you could build about 75 Pegasus-like ships for the same amount.