You can totally do it for under $500, it's just not going to be a huge flashy affair.
Venue: If somebody has a nice backyard use that for a reception. If not look at the local parks, you can usually rent their pavilions for pretty cheap and a liquor license is only $15ish. If you have base access the beach house rents for under $200. You might also check out St. Mary's College, they have a gorgeous campus and you could probably reserve a pretty outdoor vista. I'm not sure of prices.
Music: You don't need a DJ, just take your laptop/mp3 player/phone and hook it up to some speakers. I'm sure you know somebody who could loan you some if you don't have any yourself.
Officiant: If you don't want to do an actual courthouse marriage, officials can usually be persuaded to show up at a venue. My husband and I were married by the mayor in the town he grew up in. We had a lovely ceremony out on a lake and it cost us almost nothing.
Food: For food, ask your friends/family to help out and bring a dish. Veggie trays, meat/cheese trays, crockpot meatballs, dips, chips... just do heavy hors d'oeuvres. If you really wanted to provide a full meal I'd do DIY BBQ (burgers, hot dogs, pulled pork, etc). You can get paper plates, plastic knives/forks and cups for pretty cheap at BJs (if you don't have a membership they send out things monthly with a free 7-day trial membership). If you're not planning on doing this RIGHT NOW you can also keep your eye out for sales and coupons. Chinet usually offers coupons on their website, BJs also offers coupons for this sort of stuff pretty regularly, especially now with picnic season approaching.
Invitations: Print your own! You can order fairly nice stationery for reasonable prices and run it through your printer.
Photography: Photographers are expensive. Yes. We compromised at my wedding and only had the photographer there for about half of it: the ceremony, and the beginning of the reception with the cake cutting, garter toss, etc. We bought disposable cameras and put them out at each table and then just got CDs of all the prints. You might try looking for student photographers who are looking to build their portfolio for lower rates, and then see how much they would want to just be there for an hour or two to get all the important bits.
It's totally do-able, you're just going to have to put a lot of the legwork in yourself. Good luck and congrats
I have planned the whole wedding because my daughter has a great but consuming job. I still say, in the end, after 'the day' is over, I just want all to live happily ever after.
