Is the conference at the WDW Swan or at the WDW Dolphin? Although the two hotels are adjacent to each other and are marketed as a single entity, each has its own convention facilities.
Putting the official street addresses for Pop Century, WDW Swan, and WDW Dolphin into the Mears Taxi Fare Estimator (
http://www.mearstransportation.com/taxi-services/taxi-fare-estimator/), I got the following estimates:
Pop Century to WDW Swan is $7.81
Pop Century to WDW Dolphin is 8.82
Actual fares are likely to be a bit higher because the porte-cochères where the cabs picks up and drop off are not right on the streets. Also a tip for the cab driver is customary. I think you can safely use $10 per trip for planning purposes.
Renting a car just to get to the Swan or Dolphin will cost more than taking cabs, especially when you consider that there's a hefty parking fee at Swan and Dolphin.
One big advantage of Pop Century over Swan or Dolphin is being able to use Disney's Magical Express for Orlando International Airport transportation.
Then again, if the conference has group rates at the Swan and/or Dolphin, you might want to consider them. Swan and Dolphin provide an experience along the lines of Disney Deluxe Resorts. Pop Century is just a Value Resort.