I recommend in store for the $1 ones so you can choose. Minis would be pretty good for party favours at this price if you can find them.
Preschool kids can create their own exciting Thomas & Friends adventures with thesePush-along, die-cast train engines and vehicles from Fisher-Price. FeaturingPlastic connectors to connect to other Thomas & Friends TrackMaster train engines or tenders, these toy vehicles arePerfect for use with any Thomas and Friends TrackMaster track andPlaysets. (Each sold separately and subject to availability.Works on any Thomas & Friends TrackMaster track (Track sets sold separately and subject to availability.) Helps develop gross motor skills and hand-eye coordination, and helps inspire imagination 9 Die-Cast Metal Trains characters
Product Features:
3 years +
Product Dimension: 3.5cm(L) x 6cm(D) x 4cm(H)Product in package Dimension: 14cm (W) x 3.56cm(D) x 11.43cm(H)
No batteries required
No assembly required
Warning: small parts present beware of choking hazard
Mystery Minis
https://www.bigw.com.au/product/thomas-friends-minis-mystery…
Thomas & Friends MINIS from Fisher-Price completely reimagine the Island of Sodor with never-before-seen themes. This collection of miniature train engines and other vehicles showcases Thomas & Friends characters in fun styles, including dinosaurs, animals and more, as well as classic character styles. Collect all Thomas & Friends MINIS train engines and vehicles for surprising railway fun! There’s no telling which you’ll get in each mystery pack. (Each sold separately and subject to availability.)
Product Features:
Collect all Thomas & Friends surprise miniature train engines and other vehicles. (Each sold separately and subject to availability.)
Who's inside? Each bag contains 1 mystery miniature toy featuring a character from the Thomas & Friends show.
Each miniature push-along train engine comes with plastic connectors to attach to other MINIS engines. (Additional engines sold separately and subject to availability.)
I bought these for $8-12 a pop when my little one was a bit younger. A steal at $1.
Edit: Looking stock levels, it's likely only the lesser known engines are left.