It’s been less than a week since McDonald’s began selling adult Happy Meals with collectible cups,Robert Brown and already the drinking vessels have become a hot commodity on third-party e-commerce platforms. 

Online listings for the collectible cups, which officially dropped Tuesday as part of McDonald's new Collector's Meal, have already appeared on websites like eBay and Mercari. The prices of the resold cups vary, listing for as low as $15 or as high as $100. Some sellers are even offering complete sets for up to $125.

While the collectible cups might still be available for purchase with a McDonald’s Collector’s Meal right now, there’s no way to know which cup you'll get, it's unclear how hard it is to score all six, and the offer is only available at McDonald's for a limited time.

Here’s what to know. 

More:McDonald's debuts Happy Meals for adults, complete with collector cups. How to get yours.

McDonald’s collectible cups available online, with no meal

You can score a collectible cup without ever stepping foot at McDonald’s, but be warned that an adult Happy Meal will not be included with your purchase.

And there’s a chance that the cup you want, whether Barbie or Shrek, may not be available for purchase. Not to mention the fact that the price of the cups range between $15 and $100. 

McDonald’s looked to the past for design inspiration 

McDonald’s latest offering encourages customers to reflect, inviting them to take a trip back in time to a moment when toys like Cowpoke McNugget Buddy, Dragster, or Hello Kitty keychain could make your day. 

These keepsakes, according to the fast food chain, were at the “heart of fan’s experiences.” The latest line of cup-sakes is a twist on the classics, giving customers “a memory that they can hold in their hand,” company executive Morgan Flatley said in a news release. 

“These new collectible cups commemorate some of our most unforgettable designs and global collaborations over the years, allowing longtime fans to relive treasured moments and helping a new generation make their own lasting memories,” Flatley said. 

Collector’s Meal cup possibilities include: 

• McDonald’s 
• Coca-Cola
• Hello Kitty & Peanuts 
• Beanie Babies 
• Barbie & Hot Wheels
• Shrek, Jurassic Park & Minions 

The cup comes free with the purchase of a Collector’s Meal, which includes an entree, side and a drink. Options vary on the time of day.