My cheat sheet with a comparison between all of the healing items: https://drive.google.com/open?id=1-OAxIbhM-KS4yjifDLSn5kqHdAccrGP7n2l8hJ_PPC4

This not only compares all of the bought items, it also considers the prices (and crafting times) for items that were made using the Medstation.

Except for the Salewa (which is made by combining Painkillers, Splint and Bandage) all of the crafted healing items are made from "Pile of meds", which is made from Car medkits.

"Crafttime full heal" is the craft time in Minutes it theoretically takes to fully heal you after you died. I know this is only a theoretical number, but it is still important when deciding on which item to use.

My recommendations:

• First heal with bought AI2s
• As soon as you can, use Salewas crafted with the Medstation
• Once you can, buy Car medkits, use them to craft AI2, use Car medkits if you die more than you can craft
• In the end use crafted (or bought, if lazy) Grizzlys

Like u/Dazbuzz pointed out you can use Car medkits with low durability to make Grizzlys and AI2s, which makes them even cheaper.
You can also sell Salewas in the flea market.

Please tell me if you discover any mistakes, I'm only level 8, I can't personally check most of the numbers.

https://preview.redd.it/yctgsv4yt9z31.png?width=722&format=png&auto=webp&s=79820b5f5a6e90e9ca0cc5ec87bf14983570dc09