Well, a few things.
One, ebay won't help. The Sims 3 games require a S/N to install and that will have likely been used to install the game already if the game is used, so I'd avoid used copies unless you like paying $30 for a DVD case. And new prices are roughly retail price right now.
Two, the prices will go down... in about 3-4 months or so. Pets launched in October and was around 10-15 bucks around Christmas. But that doesn't help you now.
Right now there are no active sales for Showtime, so you're basically out of luck. You might trade in a couple of games at GS or BB to get some trade-in credit, but that's about the only way to reduce the price right now. Sorry.