If you are telling people it's BYOB and potluck, ask people to bring either a sweet or a savory finger food type thing - be specific about which one. and a good hostess is always prepared for the just in case...
$20 fresh flowers
$10 paper napkins, plates, cups
$5 bags of ice
$20 a few beers and a bottle of liquor for yourslef and those who forget.
$10 ingredients for a big pan of baked ziti with cheese and sauce for those who are really hungry
$15 ingredients for a big garden salad
$5 extra toilet paper and paper towel
total: $85
add and subtract as wanted!
fun music (have your friends bring some too - and folding chairs if they have them!), lit candles and good lighting, a clean bathroom and empty garbage cans... priceless.
I forgot about the 80s theme:
$10 flourescent colored streamers and balloons.
$10 a game of Twister if you have the room
play 80s movies in the backround on your tv
i tend to think that as long as people are dressed to impress and the music is 80s fabulous - the theme is pretty set.
have fun!