PLEASE NOTE
Postcards are obviously thicker and heavier than stamps - this means postage costs are probably higher, especially if more than 1 set is bought.
In addition , any package thicker than 5mm falls into the LARGE category for Royal Mail postage.
Lastly, please remember ebay charges me fees on postage too :-)
UK : Weight <100g and thickness < 5mm £1.50
Weight >100g or thickness > 5mm £2.00
Weight >250g or thickness > 5mm £2.75
ABROAD :
Weight <100g and thickness < 5mm £3
Weight >100g or thickness > 5mm £5.00
Weight >250g or thickness > 5mm £7.75
I came across a site which has lists of Vatican AEROGRAMMES and POSTCARDS ( www.vaticanstamps.org : register and you can access the lists )