Posting as a regular parcel shouldn't have cost any more.

If you are using your own packaging and not the satchels or flat-rate boxes, then the postage cost is the same whether you use C&S or not. Adding tracking in C&S costs $1.55, the same as buying a tracking label over the counter.

The only difference is in C&S you can add tracking to parcels over 250g whereas if you buy tracking over the counter the parcels have to be over 500g.