If you process the label via eBay or Click and Send, you can purchase a label for a 500g standard parcel (a bit over $7), then add the same options - signature on delivery and insurance. The insurance is what will cost the most, because it's $1.50 per $100 value (or part thereof).

So, $7.45 (from memory, for a non-eBay satchel parcel)

+ $2.95 signature on delivery

+ $15.00 insurance

$25.50 for regular, platinum express would actually be quite a bit more.