Value is hex.
2 methods of search. Use the text search feature and search the price of one of the elixers. The text search is not UTF-16. When you get your results, do not replace. Scroll to the last result. The 56 byte value, edit to 45 (change the 8 to a -). Now the price is negative 500. If you want edit the dword 4 above to dword 8 (this is number of digits in price) then edit the next 4 bytes to 48 to 57 (48=0 57=9),I did all 48. Price is now negative 5000000. If you want to go larger, you can, just the next dword needs to be 0 following the price.
The other search, byte search 4D;56;53;48;48::10 and following same steps as above for editing.
I don't know max gem value, but it's over 2147483647, so no worries on that.