Congrats to you and your fiancee!!! YAY!!! :)
Well the main thing is to do what you can yourself... invites, flowers, favors, decorations, etc... those little things can add mucho dollars when you have someone else do it!
I have a budget myself of $4000-5000 (hopefully closer to the $4000!) and I'm having about 125-150 guests.
The biggest expense is the meal/bar bill, which is usually about half of your budget. Having a buffet might be a little cheaper than having dinner per plate, I think mine's gonna be about $10-12 per guest for dinner. As for the bar bill... I'm going to pay for soda, get a keg (or perhaps a half keg? I'm not certain yet lol) of beer and if anyone wants mixed drinks they will have to pay for them. (Some people may think it's tacky, but I am actually putting on the invites -- in small print at the bottom -- that a cash bar will be available all night, so they come prepared, cuz I know a lot of people won't bring money with them if they think *everything* is complimentary.) Mixed drinks are what really hikes up your bar bill!
You can get a lot of ideas just watching those bridal shows on TV. I've also gotten a lot of ideas just reading people's questions and answers on HERE.
My cake... I actually was lucky enough to come across a girl on Myspace that lives in my town that does beautiful cakes out of her home for relatively inexpensive. BUT you must watch that, only cuz a lot of reception sites require a licensed baker or to use their own on-site baker, plus there might be a cutting fee which can range from $1-5 per slice (or even more!!! Make sure you read the fine print before you commit!) :) Also don't look past going to Walmart's bakery or your local grocery store's bakery... I've seen some great cakes come out of those places too, and you would have never known it!!
I am making my own flowers. I actually hit Hobby Lobby when they were having a 50% off sale on all of their flowers, so I got $100 worth of flowers for $50! You and your bridesmaids could have a flower making party (or a favor making party as well!)
As for my favors, I'm doing a couple different things. Of course I'm having bubbles! I got plain bubble bottles at Dollar Tree for $1/dozen (CHEAP!) and I actually found a girl on ebay that prints up labels for very cheap! this is a link to the seller http://stores.ebay.com/Beautiful-Favors-Fast_W0QQssPageNameZstrkQ3amefsQ3amesstQQtZkm
As for my other favors, I saw a cute one on a website for sale that was called a spoonful of kisses, and it's a plastic spoon with a few hershey kisses, wrapped in tulle and on the tag it says "A spoonful of kisses from the Mr. and Mrs." with our names and wedding date. I also am having programs which I am printing myself.
Also printing up myself are the invites! I didn't need paper that was real fancy so I went to Office Max and got some fall themed paper (cuz I'm having a fall wedding) and some envelopes and some postcards for the reply/save the date cards. (I'm only sending save the date cards to people that live out of the area that will have to make travel arrangements) Cuz I couldn't see spending a fortune on invites that most people keep until the wedding and throw away!
Also, here are some websites that I am using to curb my costs:
http://www.bridalonlinestore.com/ <---AWESOME dresses at a fraction of the cost of traditional bridal shops, excellent customer service and the dresses are JUST beautiful, and are guaranteed for satisfaction!!! They also have bridesmaid dresses as well and other accessories (veils, headbands, hair clips, gloves, guest books, etc.... you get the idea!) :)
http://www.orientaltrading.com/ <---sign up to receive their wedding ideas book in the mail (it's free!) and there is awesome ideas in it and on the website for favors, decor, etc. I'm having a fall wedding and I'm getting leaves to scatter on the tables from here (those are under the fall section rather than the wedding section though) everything is relatively cheap and if you order over a certain dollar amt you get free shipping.
http://www.tullesource.com/ This is awesome for inexpensive tulle and they have such a wide variety of colors. My wedding colors are apricot and sage and they actually have my colors in tulle, which is great cuz I need tulle for one of my favors and for my centerpieces.
http://www.confetti.com/ another great one for confetti (hence the name lol) and other decor. very reasonable prices!
http://www.michaels.com/ yeah... awesome wedding stuff for not too much! I love going to Michael's! (Hobby Lobby and Dollar Tree are my friends too!) :)
Other great sites to check out:
http://www.blissweddings.com/
http://www.brides.com/
http://www.ewedding.com/
http://offbeatbride.com/
http://www.theknot.com/
http://www.ultimatewedding.com/
http://www.weddingchannel.com/
http://www.annsbridalbargains.com/
http://www.efavormart.com/
http://www.favorideas.com/
http://www.getmarried.com/
There ya go, that should get you started!!! :)
Good luck!!!