Buy or Build or both ?
There are several ways to get a mini ;
-buying, building yourself, let them be build ?
-new design, stock design, old design ?
-or renting one ?

 Buying second-hand;

You can buy second-hand, this can bring problems or gives you a great boat for a bargain!

There are two ways;
You buy the winner's of last time, not cheap and likely to be fully equipped, potentially in a good shape but may need refit having raced across the Atlantic.This will save you a lot of time instead of going for designing and building a Prototype from scratch.

Youcan buy an older one, this will be "cheap" but can bring problems.Both options are only advisable when you can detect structural problems.The Classe Mini designs are mostly not designed and built to last.A good survey can give you piece -of-mind.
Go to the Forum; Boats For Sale for an oversight where to get second hand boats.

Participating in an existing building program;
You could step into a programme or start one with more sailors building one boat. Like that of Team 6-5 Mills Mini (99) or the Magnen_Niveltdesign (01) build by sailors Bestaven and Boissieres. Or the Slovianian guys in 05. Saves money and you can help eachother in keeping the spirit up. You "only" have to find a kindred spirit.

Building a new boat;
Two ways to approach this.

You can commission a special design, a boat for your self, as ugly or beautiful as you wish. Even towing tank tests are now becoming a reality for "smaller" budgets.
( and yes it is a Mini-Transat racer with twin rudders is being tested at 5.4 knots and 20 degrees of heel, interesting is that the French did a lot of research in Southampton and the design changed to a wider one.)
Think over the options if you want to approach a designer, remember, it will be like creating your own 'perfect Baby' exciting but time consuming.

Or a stockdesign.
Stockplans are already available of a couple of designers, which mean that the same plans are sold to a number of people. And if you are lucky there is somewhere an already existing mould. That saves a lot of time. Then you can play with the keel, hardware etc etc.

Some are designed for backyard building. The building manual will be more detailed and the faults of the design (possible) altered. However you may need to be familiar with the language of the designer to understand and progress the plans effectively. The designers for backyard building (no composite, but plywood, I regard composites as a building method slightly above backyard. At least you have to do that indoors in most countries, smile) know off are; Jean Pierre Villenave, Dix and Rolland( the Loi et Vin type, 4th in the MT '97, the photo under shows a 2001 design of Rolland, This 238 performed less, but hey, he had tinned cans of food and a lot more weight not really needed onboard. Check the sailors site....
.Click here for a site with plans of Villenave, there is somewhere a photo of the Turbo, and building info. A Villenave sailed the 2003 race, and showed not to be slow either.(French only)
THe MIniCP from Lucas is the newest (06), its a fast one if buildright, no cantingkeel.But not provided with real building manual, so basic boat building skill you need. (just order a dinghy from Woodenboats and build one in two weeks :) ) see drawing...

The borders between a serie design or a really new prototype are fluctuating. A designer normally changes little to an existing design, mostly improving it.

 Then comes the question which designer to choose.Take a look at this page at thedesigners section for the winners of all the years of the Mini Transat.Or will you give a new designer a change ?

Another option is renting a boat for the season. But you must be a good well known sailor to pull that off, or you rent an old boat ;)
Prices fluctuate from reasonable till expensive.
A problem is the insurance and the organising skills of the owner.