SlipStream

While Slipstream is still obtainable, it's performing extremely well for a low demanded cosmetic, easily being able to be traded for other 500K items (and at times even more). This is due to it being quite an appealing cosmetic, being quite similar to Manga, except way cheaper than it, which makes most traders want to get it as a result. It's most common offers include: Roll-x, EXP-1, Bacon or Slipstream + small add (around 100-250K) for any 750K item (like Aquatic).