I bought a chocolate frog mold from
amazon for $5 as an add-on item. Very easy to make them--just microwave some chocolate chips, scoop a little melted chocolate into the mold, add a teaspoon of filling (I used apricot jam for some and peanut butter for others), then spread with more melted chocolate. 10 minutes in the fridge and they're done.
Bought two 6-packs of Bertie Botts for 11.40 per 6-pack, and an 8-pack of Wizard Glasses for $12. Also a Wizard Snowy Owl for the birthday girl for $11.
Made a cut-out of the "Have you seen this wizard" by printing on large-format paper (in two halves), plus the prisoner number. Pasted the halves onto foamcore, so each guest could have their picture taken inside the frame, holding the prisoner number.
Printed school crests, Platform 9 3/4, and "No Muggles Allowed" signs on color printer, taped to walls.
Bought a pack of 25 plain invitations and envelopes. Printed Hogwarts welcome letters, personalized to each guest ("Miss J Smith, Cupboard Under the Stairs, 4 Privet Drive, Little Whinging"), added the Hogwarts crest to the outside, and "sealed" with a printed red wax seal. The rest of the envelopes were addressed to Mr H Potter. Hung all of them from the ceiling with thread, and each guest found their letter as a keepsake.
If you like I can email you the welcome letters and fonts, and the wanted wizard poster etc.