It is expensive, so please think twice before embarking on any "upgradathon" as you can lose everything in a very short span of time.
Cash prices of Chilli Powder, Lucky Jam and Preservatives will be capped from Grade 6 onwards, but Gold prices will be higher with each higher grade. As these are originally cash-only items, the gold prices are fixed and will not be revised.
Note of Advice to Upgraders
The success of any upgrade is NEVER guaranteed. There is always a variable success rate for each upgraded level which gets lower with each level of upgrade. As a guideline, chances of success for each upgrade beyond +5 is always less than 50%. It is possible to fail more than 10 times in a row, it is also possible to keep succeeding. It is all based on luck!
Use your Chilli Powder with caution and know when to stop. Being too rash or greedy may let you end up with +0 and no Chilli Powder left.