Good info by async.
As a beginner to intermediate rider, I would worry the least about the board. I used to hear of so many spolied kids in HS getting the newest $400+ Burton board yet they still sucked ass. I've snowboarded for over 7 years, and I'm STILL using a Division 23 ~148cm I got used from a friend for like $90. It is starting to get some chips around the corner but hopefully it will hold up until I graduate college. One of my roommates now had this Div23 board for like 3 years (this was like 6-7 years ago), sold it to a friend who used it for one year, and now I've had it since. Really unless you have a piece of crap board, it has very little bearing on how you snowboard until you get very good or you want a specific board for rails or whatnot. I've noticed just a small difference in friends' boards I've rode and that was mostly because of length and flex differences. My first board was a Type A that was rather cheap as well. For the board, I would check out local shops for last-year models and clearanced ones. I never got why people think they need the newest Burton board. Just find the right length board, or you could even order online.
So depending if you get it used or clearance of course, but I would say no more than $300 for your board but closer to $200 possibly Again, I bought my current one used for $90 and for 7 years it's been rode by all kinds of people in all places and just now is starting to show signs of significant wear. Just get a relatively name-brand one, preferably good condition used or closeout. Doesn't have to be the "top shelf" ones like K2, Burton, Ride, Forum, etc.. Stuff like Division 23, Type A, would do and god I can't remember osme others, but Performance Snowboarding used to be an excellent internet retailer with good mid-range equipment. Most important is to get one that matches your height and weight, riding style (freestyle you'll want a more flexible and shorter board, but for speed and just carving down the hill or freeride, longer and stiffer is better)
Bindings.. just don't get some cheap ones with no support and padding. I'm using my very first Burton bindings that cost about $130 7 years ago. I've replaced the hardware on them a few times and that's it. Can't really complain about them, I mean they work. Maybe in 1-2 years I'll get a new board + bindings. Again, possibly check last-year or clearanced bindings.
And lastly I agree with the others on the boots. Try on all kinds of them. I paid about $130-$160 each for the two pairs of boots I've had since I've started. I can't remember the brand I have right now, but they are good, no complaint there either.
For $500 you can get all 3 that will be plenty good enough for years down the road.