Cutting costs on parties while maintaining a theme isn't as difficult as it seems. 

1. Make your own invitations.  There are many ways to create invitations that will introduce your guests to the parties theme and cost less than purchased invites.

2.  Color goes far to maintain a theme.  Red paper cups and plates for a Valentine parties works as well as heart covered cups and costs less.  Put the hearts on the cupcakes, napkin rings, balloons or other decorations.  The overall design makes the parties theme work.

3.  Food can be part of the party's entertainment such as mini-pizzas created by the kids at a birthday party or sundaes created by guests at a baby shower. 

4.  Gift bags for guests can be candies and trinkets in a bag stamped with colors and items from the party theme and tied with ribbons.

5.  Other entertainment ideas can go with the theme of the party.  Dress-up for little girls having a tea party birthday or decorating baby rompers at a baby shower.