Here's a link to the model you have:
24 is the European size label that is comparable to a US size 38S (the "S" is for "short"). A "short" suit is typically shorter in the arms and overall length, and for Suitsupply usually has a slightly larger chest measurement. If you visit the link above you will see a link on SuitSupply's website for a Size Advisor that has the measurements for the different size Napoli suits.
The 299.00 price likely refers to the suit price in Euro, since SuitSupply is a Dutch company.