Building a Multi Hull
There is a lot more questions to your post than my first impression suggested. To begin with you really do not explain what you intend to do with this boat, or why you and your boyfriend have focused in on a 30 foot catamarran (a multihull with two hulls), or why you are interested in a Wharram design, so it is pretty hard to advise you on comparable designs.
One reason that I say this is that 30 feet is quite small for a catamarran. Cats need to be quite light to sail well and so it is hard to build a 30 foot cat that carries enough gear and supplies for even a couple to do limited cruising before the added weight becomes a real problem. It is for that reason that most small cats are designed as pretty barebones raceboats.
There are small cruising Cats but these typcially give up many if not most of the desirable traits that attract people to cats in the first place.
Trimarrans (three hulls) actually make more sense as cruisers in these kind of small lengths that you are considering.
Which brings us to Wharram. Another reason that I say that it is pretty hard to advise you on comparable designs is that Wharram''s work is pretty unique and quite out of the multihull mainstream, and evern further out of the sailing mainstream. His designs cleverly conceived to be easy to build and examples of his boats have done amazing voyages, but in practice these are really less than ideal sailing vessels offering the advantages of neither a multihull or a monohull and a whole range of unique disadvantages. I have sailed one of Wharram''s small cats (26 or so feet long). It was a miseable boat to sail in the confined waters that are typical of coastal cruising. The simple details that made these boats easy to build, also made them very high maintenance and not very durable. The quirkiness of the designs make them near impossible to sell. (The one I knew was sold for pennies on the dollar to a man who disliked the boat very quickly and ultimately built a 36 or so foot center hull and used the Wharram hulls as the outer hulls of this 36 foot trimarran.)
In terms of other designers, if I remember right Dudley Dix of South Africa used to have a neat little 34 foot or so Trimarran design which I don''t see on his site anymore. His prices should be pretty close to those of Wharram but his designs are a lot better suited for most people''s uses. Mr. Dix can be reached at http://dixdesign.com/
I have also liked Chris White''s work. He is a very pragmatic designer who produces very high quality designs. Although his web site seems to focus on big cats, I beleive that he had done some small multihulls years ago. I like his Juniper'' design but it may be too big for you. http://www.chriswhitedesigns.com/
Probably my favorite Multihull designer is Dick Newick. I have always loved his creativity and the beauty of his boats as well as their trendous sailing abilities. http://www.wingo.com/newick/
Perhaps another (and better than Wharram) way to go if your goal is cruising would be to look at something like Jay Benford''s Dory series. This is a monohull. His 34 foot cruising dory is a ''go anywhere'' design that can probably be constructed more easily and for probably about the same costs as the Wharram that you are considering. This boat was featured in Anne Hill''s book ''Voyaging on a Small Income''. She did a Chinese Junk rig but the cutter rig (or even a sloop) has always looked very appealing to my eye. The price for these drawings are about a third of the cost of the Wharram plans and when you get done you will have a boat that you might be able to sell again some day. (Benford even has a set of very inexpensive ''bid plans'' which are just complete enough that you can develop an approximate construction estimate.)Jay Benford can be reached at www.benford.us
On the subject of the cost of the drawings, $1,500 is actually a pretty good deal. A custom set of drawings typically cost around 10% to 12% of the retail cost of constructing the boat. A boat like a 30 or so foot Wharram would probably cost something in the neighborhood of $60,000 to $100,000 without sails or instrumentation (the materials alone could easily run something approaching $40K) to have professionally built so $1,500 is a real bargain.
Given the major investment in time and money to build a boat, I cannot recommend too strongly that you take your time and pick a design very carefully. I cannot tell you how many times I have watched someone spend years and years of thier lives building a boat, only to find that it is really not even close to an ideal design for their purposes.
Lastly, unless you have your hearts set on building a boat, which of course is a valid reason to build one, you can often find a used boat of a similar design for far less than the cost of building one new, and rarely will you see a dime at resale toward the value of your time.