Can you provide more information? Primarily, what is the volume of the outer hulls? The current rule of thumb is that the outrigger hulls should have a volume of 130% or more of the loaded displacement. I emphasise loaded because Multihulls Magazine once listed the published and measured weights of several production multihulls. One boat had a measured empty weight just above its designed displacement.
I also remember seeing a calculation comparing trimarans and catamarans with and without bridgedeck and with fat or narrow hulls. The configuration that minimised skin surface area (one component of weight and cost) was the catamaran with fat hulls. Derek Kelsall used to have a line of designs like that. If you want the most living space from a given amount of money, the trimaran may not be the way to go.
Edit: I finally remembered that this series of Kelsall designs was called Tonga. I found an example at http://www.xboat.uk/318-DEREK+KELSALL+CATAMARAN+TONGA+TINI.html. Pictures 8 and 9 show most clearly that the hulls are fairly broad for a catamaran, and the omission of a bridge deck, the idea being that if you wanted more inside volume, it would be better to put that into larger hulls instead. The stock designs now Kelsall's web site all feature bridge decks, though. I suppose most customers dislike the idea of having to go outside to get from one hull to the other.
Also consider that trimarans need to be a bit wider than catamarans of the same length. The reason is that trimarans sail at a greater angle of heel because the lee hull submerges more than that of a catamaran, and that a beam sea will still lift the centre hull of a trimaran when it has already passed the weather hull of a catamaran of the same beam. Therefore, if you want the trimaran to be as safe from being flipped by a wave as a catamaran of the same length, the trimaran needs to be wider. That adds to loads and weight.
What I would study in detail, given your design brief as I understand it, is a very wide Pacific proa with a low volume, high density windward hull, a single stayed mast and junk sails set on the stays, including the windward stay. The latest AYRS Catalyst contains an article on why that rig theoretically should give good helm balance and pictures of a rudderless radio-controlled model that I could steer by sail trim only. I could upload a copy of the article here (once I look into how that works). I am even considering this for my next boat, only I have the additional constraint of a small harbour and a berth limited to 9 m x 2.8 m, not the 9 x 9 m that design should have. I would have to fold the boat up as well, driving up cost. And payload would be roughly that of a 6 m long catamaran. So even if the proa were to cost less to build for a given payload and speed, it has a large footprint, which makes for high berthing costs. If you will keep the boat on a mooring, this may not matter. I don't have that option.