I have found a big way (through reading on these boards) that to cut costs you cut your guests which is very logical. BUT I have also seen on these boards people up in arms when someone doesn't want to let BP/friends/family/etc invite a date/child/friend because they can't afford to have them there. So which is it?
If your guest wants to have someone tag along that you either 1. don't know 2. don't like 3. didn't invite you just say ok well friend that I did invite, you are not invited anymore because you are going to be wreaking havoc on my budget. (Also I'm not talking about one person tipping the scale but multiple "guests" doing the damage to your budget.)
Or do you be polite grin and bear it let them invite whomever because you're not supposed to break up families/couples/social units/etc and let the damage be done to your wallet?