My situation, as well as Adam and AJ's, was a bit unique.
I was approached by a very generous individual who works with a wounded veteran non-profit on a volunteer basis. This individual agreed to loan me his boat for the race, with basically no strings attached. The non-profit had a program that grants a "Warrior's Wish" to wounded veterans. I qualified for the Wish, so I said my wish was to race the SHTP, and as such, I asked for them to pay my entry fee and buy a SSB, auto tuner and radio modem. This came to 5 grand in total. So truth be told, I wasn't really "sponsored" by the non-profit. I was granted some funding which was actually available to any wounded veteran who qualified.
On top of that, I had a boat yard pull the boat off the trailer, give us a few days of yard time, and then splash us for free. The marina gave me a free slip, I got 1 gallon of free bottom paint, free foul weather gear and PFD, and some free halyards. I got some free video cameras, discounts on batteries, discounts on this, discounts on that. Pretty much everyone that sponsored me was either just super nice and wanted to support me (a wounded veteran) and what I was doing (raising money and awareness for a wounded veteran non-profit). I approached every sponsor individually, generally with a packet containing pictures and information about what I was doing. Some people never replied, while some said "sure, what do you want?" and some said "we'll sell to you at cost.". Getting stuff at cost can be a good deal, often times 75% off of retail. If this can cover the additional $900 or so in entry fee (for being sponsored) then it's a good deal. It costs a sponsor nothing to sell to you at cost. Free exposure for them, so it' s a win-win.
I am working on some big time sponsorship for 2012, but it will be completely different and will again be a situation that is rather unique.
Having said all of this, I would not advise you to rely heavily on sponsorship. The race does not have much of a media presence, and a sell for big sponsorship will be difficult.
All in all, I would say Warrior's Wish spent 10-15k on the race, and that doesn't include any new sails. The boat was already more or less entirely equipped, just requiring some parts being replaced, boat repairs, maintenance, etc. It's definitely not a cheap endeavour and I will bet that most competitors went over their budget for what they originally thought it would cost. I know I did. It wiped me out this year and i'm still getting back on my feet financially.
But it was most definitely worth it.
Good luck on your campaign in 2012.