Bimmerbill.. I only know a little about this and can't help with the funding aspect.. Nephew (now 6 and in "regular" 1st grade with a full-time shadow/assistant) was diagnosed autistic/Asperger's. My sis investigated ABA but it is not necessarily a panacea and is very costly and intensive. Sis was ready to fly to Denver for an RDI seminar (which she didn't ultimately do as her "DH" would not have been reliably on board anyway, and it is very much "family"-based, apparently, sadly not appropriate for them for certain reasons better left unexplained further). I have experienced many of my nephew's meltdowns and behaviors outside the norm since he was born; I'm not sure that rote ABA training would do more than superimpose a band-aid of programmed responses on an otherwise-unconventional nature or psyche. RDI seemed more of a baseline emotional "re-connecting" rather than a (what seemed to me as a more superficial, yet more "accepted" by "the system") mechanical "training" ABA approach. I think the RDI people have a DVD available for review.
Learn and Grow: Understanding RDI with Connections Center
She also looked into the "DAN" therapy model.. ultimately she hasn't opted for any of these 'proprietary' approaches but has relied on the public system so far. But her son is now relatively 'high-functioning' at this point.
A number of my nephew's "unacceptable behaviors" have abated somewhat with age and maturity. His meltdowns are fewer, and he's apparently not as super-sensitive as he had been. But he (and, to a small degree, his sister) still has many "issues" with not accepting authority, not buying in to the "master-apprentice" model, and basically perceiving every-day life as throwing a monkey wrench into his works (or he throws a monkey wrench into daily life.. depends on how you look at it!).
Sis has found decent-but-not-overwhelming support through the public school system (an Early Learning Center and enough people at least vaguely attuned to the issue). The level of support is, of course, a function of the community and their prop.tax structure (she is in CT and pays $8-9+k/year living in a very average house).
When nephew was in the (public) Early Learning Center in CT there were kids not as verbal/advanced as he but they all seemed to get quite a lot of attention and care: "occupational" therapy, language therapy and sensory therapy all.
So don't give up entirely on the public system as yet; depending on where you are they could do a yeoman's job, and it might be up to you, based on your choice, only to supplement where necessary/appropriate outside of the hours where they can care for your child.
You and your wife will in any case need to be aggressive and vocal advocates for your DD.. You're "lucky" in that the NE is a bit more progressive and you'll find more treatment centers, support groups, awareness, and so forth than in some other areas of the country.
A few sites I collected over the past couple of years are here:
Wrong Planet Forums
MOM - Not Otherwise Specified
29 Marbles
Adventures in Autism
Autism Support Network | Connect. Guide. Unite.
Autism Speaks, Home Page
There were a few other interesting ones that have gone down the memory hole and are no longer active.
Some people think diet, vaccines, environmental toxins have a role; others not so much. Some report improvement with the removal of gluten (wheat protein) and casein (dairy protein) but this is in no way universal.
Another thing my sis was attracted by, but has not tried, was a kind of biofeedback, more or less.. sorry I can't find the link right now, but there was a practitioner in/around CT. After I speak to her in the next day or two I will try to post a link on that...
You'll find yourselves immersed in the world of "special-ed-speak", IEPs and so forth. Get to learn the baroque angles of this "educator speak".. learn the (often apparently quite stupid) ropes. There are key words you can employ as "triggers" that school authorities legally have to respond to. Many parents have recurred or at least feel the need to recur to lawyers in order to get their children's needs met according to the law. Overburdened school systems will drag things out and attempt to kick the can down the road. Sis sent me letters to review where I marveled at the language she used, but what I pointed out as odd phrasing she assured me was targeted "educator-ese", eg., "social typical peer immersion".
You'll have to learn and implement to the best of your family's advantage what is meant --technically, EXACTLY, literally and legally, to the particular school system you are dealing with-- by "need", "placement", "environment", "assistance", "monitoring". "services", "development", "behavior", "regulation", "processing", "support", "intervention" and so forth.. on and on. You may find info on autism forums that point you to more receptive school districts; it seems outside of those there isn't really any material public support. Autism seems to be labeled a psychological/psychiatric disorder more than a direct health issue.
Sis ran into the Catch-22 that no-one wanted to diagnose at a young age.. yet, as you point out, an early diagnosis could be very important. Her ins. co. refused to even make psych. appointments for kids younger than 6, IIRC so she ended up paying out-of-pocket. Then perhaps a limited number of visits with limited doctors, that she hasn't bothered to take advantage of. Neither do they cover any alternative therapies, should she want them.
Best of luck, and I'll try to get back on the biofeedback thing.