score:7
I see you've already found Perama, which is the largest cruise/ferry operator around Lombok, and they're quoting Rp 1.3 million for a deck fare, which sounds about right (~US$110). There are other operators, but I doubt you're going to find anything substantially cheaper, and if you do it'll be cheap for a reason (unseaworthy boat etc). Even Perama is kind of dodgy, but hey, Indonesia 'gitulah, it's either that or fly and Merpati isn't much better.
What you can do, though, is negotiate your own package where you just combine the dates/bits you're interested in -- since there are 4 to 6 of you, you'll have a fair amount of bargaining power. I wouldn't even bother trying to sort this out beforehand, just show up at the Perama shop in Labuanbajo and see what they can do.
Upvote:3
As pointed out by jpatokal
, those sailing boats are rather unsafe. Now if you still decide to continue with this decision, please find details about it below.
There are actually different sailing options:
Price for all those options is between 1.3 & 2 million IDR, depending on the company & your negotiating skills. Do shop around.
Departure dates:
Sailing boats leave almost every day, but each company usually have only a couple leaving each week. So do shop around to have the most options for departure dates.
When booking:
Finally, do not expect anything contractually written regarding the journey, it's all very informal & it does not look like it's about to change. Try to speak with an employee who actually knows what he is talking about, most have never been on this trip & would sell you anything. Ask questions such as: number of passengers on board, all planned stops and activities, food included, drinks included, arrival points, & so on.
Dangers and insurances:
If anything goes wrong, none of the companies will refund you. They will however take you to the end destination whichever way they can for the rest of the journey, most likely by a combination of bus and ferry as described in Go from Lombok to Labuan Bajo by bus & ferry, how to? . There are accidents regularly, whether it's a boat hitting a rocky reef, an engine exploding, or else. So be warned, this can happen to you, this risk is part of the trip. Welcome to Indonesia!
Usual path for 4 days & 3 nights:
If the trip is shorter (whether 3D2N or 2D2N), then they just remove some of those stops/activities.
You can also go by plane, or bus+ferries.
Read more about those options on What is the safest and cheapest way to see Komodo island, leaving from and returning to Bali?