Equipment
Drysuit $1000
GPS $200
EPRIB (personal) $250
Strobes/Flares $50
Camelback $30
Life Vest (Type I) $100
Spare set of control Lines $200
Spare parts $500
Backup sails $1300
Repair equipment $150
Does that sound about right?
I'd consider backup rudders essential, as they fail more often in distance racing. If your rudders fail, it will be at the start, and there will be noone available to help you (and receiving outside assistance while racing will disqualify you).
Backup sails can be an old set. I wouldn't consider them to be a distance racing cost per-se. You can surely survive without them, buying an old set after a leg from another team if you must. This way, the "cost" drops to the "insurance cost" for replacing sails. In other words, if there's a 10% chance you must spend $1000 buying a used main from another team, the expected cost is $1000*10% = $100.
You're more likely to need backup centerboards than sails, IMHO. These will also probably be harder to obtain. (Racers often upgrade sails, but not CBs.) Since there is almost no tacking in the Tybee, keep 1 centerboard up to protect it.
Does anyone actually race in a type I PFD???
I don't consider Drysuit+GPS+LifeVest+flares to be budget items, because I regularly sail with these.
I've never heard of control lines failing, unless they are really neglected and you shouldn't have been sailing with them in the first place. (Hand-held lines tend to be way over strength for the loads, so the lines are big enough to hand hold.) However, you should have relatively new standing rigging for a distance race, you should seal the swages of new rigging with bee's wax or epoxy (before the first sail) to keep out the salt, and you should have at least one spare trapeeze wire + fittings. Bungees fail for all sorts of reasons, so have spares.
Chicken lines are a must. Backup chicken lines are a good idea because you can break them in a capsize. (I did.) Fortunately, these are cheap small diameter lines. (Such as 1/4" chicken lines and 1/8" Prussicking knots.)
If you have a snuffer, a spare spinnaker sock is a good idea. (We blew out ours in a Great Texas 300 bow stuffing incident.)
I believe the Tybee requires lifelines, which are a 'beener, some bungee, some tube nylon webbing, and a snap shackle, so you can stay attached to the boat at all times. That's about $40 per person.