Can you send as a registered letter?

Small prepaid envelope

DL, 130 x 240mm
Up to 500g

Buy 1: $17.70
Buy 10: $16.83 each
Buy 50+: $15.94 each

Or maybe just send as a letter without tracking and take the chance of losing a few?

Letter (50g)

Up to 260 x 360 x 20mm

Up to 50g

$3.40

Letter (125g)

Up to 260 x 360 x 20mm

Up to 125g

$8.30