My daughter spilt green tea on the Macbook - it's toasted and we will be receiving a new one along with the HDD from the old machine- whats the simplest way to recover the data (assuming it is working)
1. (B) There is a cheaper, albeit tedious alternative. Assuming your replacement MacBook Air is the exact model as the old one, you can always open the new MacBook Air (possibly voiding warranty if things go awry) and install the old FUNCTIONAL SSD and transfer the data you need onto an external hard drive. Reinstall the new SSD and voila. https://www.ifixit.com/Guide/MacBook+Air+13-Inch+Early+2015+SSD+Replacement/38535
2. The MacBook (assuming you're talking about a black/white plastic body OR unibody MacBook), has an HDD... If its still functional, you can also find a 2.5 inch enclosure at most computer supply stores and transfer that way.
The first few Macbook Air models had HDDs, (and they were rubbish.)
If you are receiving a new MBA, I would be extremely reluctant to void the warranty by opening it up.
We need to know what year your old MBA is before we can advise further on enclosures. If it uses SSDs, then one solution could be to ask your repair shop to transfer the info onto a flash drive or normal SSD (ie. non-Apple SSD).
You can sell the old Macbook SSD - they are highly specialist items and bring in a fair bit on Ebay. The repair shop might be willing to make you an offer for it.