A lot of my thoughts and suggestions are already echoed but most of the costs that are still due seem to be things you aren’t fully on a 100% fixed cost for so you are lucky on that. In addition to what is suggested, have you thought about only inviting adults and changing the guestlist? Eliminating children and those “extended” members could help out a lot.
to go line by line on what can be helped:
Caterer: $3500 – (pot luck this or negotiate to see if anything can be changed, even cutting minor stuff could be highly effective. $1 per person is still $350! so 50 cents would be $175. Every little bit counts. Or make just appetizers and then you can put the money towrads the liquor if that’s what you feel is more important. Also could eliminate the need for as many chairs and tables. Make it standing)
Beer and wine: $1000 – (BYOB or nix all together. Are they really your friends if they wil be offended without liquor? The last few weddings I’ve been to were cash bars and no one was offended. In fact, if you tell people that they can bring their own alcohol they might like it better cause it’d be more cost effective than having them pay per drink at a cash bar. I think I was even at a wedding where someone brought a bottle of vodka to the hotel room and drank before heading to the reception. Not a big deal at all! Especially since it’s your parent’s property)
Fiance Suit: $200 (Try to rent or stop scavaging through ross/burlington coat factory/marshalls/nordstrom rack/ebay/etc. OR you can see if he knows someone of a similiar size he can borrow from)
Plane tickets: $500 (Call the airline and see if a lower rate comes up or what the cancelation fee is. Or plan a few days ahead and drive the distance. I know CA to CO isn’t exactly close but the gas will be much less and you can haul stuff with you to save on baggage costs and stuff like that)
Shoes: $150 (see if you can exchange these for something less expensive. Especially if your shoes don’t even show)
Band: $1500 (check to see if you can have a smaller band and get a portion of it back. Maybe you can change it so you only have a few members and reduce the cost? Or see if you can cancel it and find a cheaper DJ or another band on craigslist or something)
Cupcakes: $500 (Depending on how many you are ordering, see if you can get a refund on it and then make your own or have some of your friends help you? or family help out? You already said you are ordering less than what is needed so it’s completely do-able)
Tables, chairs, table cloths, silverware, plates: $2400 (Depending on whether you rent or bought them or whatever the situation is, figure out what the cancelation or change fee is. Maybe you can change it to a standing reception or change it up for cheaper chairs? or cheaper options to each one.)
Lights (for outdoor reception): $500 & Candles & Votives: $100: Pick one or the other…. Even a $100 saved is $100 you don’t have to spend. That is providing that you can return these items.