There is no exact answer of this question. If you are a small business or a giant corporation, your budget should be different.
If you are a beginner to Amazon PPC, your starting budget needs to be large enough to give you an adequate amount of data. You have to collect a data to optimize your Ads in future. Amazon PPC is a long run competition that will never ends. Every data you collected is your strength and the budget you have is your stamina. You have to optimize both of them.
The easiest way to get started on PPC is setting a budget that generate 20-30 clicks per day. You may use Amazon suggested bids for a reference when setting a campaign. You have to start with auto campaigns and you shouldn’t set a manual campaign with hundreds of keywords. You have to expand your knowledge of the market step by step and bid accordingly to avoid waste of budget.
As conclusion, in every market and situation the money you should spend vary. But the suggested PPC budget is 10% of your total revenue. You should never forget that organic and paid traffic affect each other and your revenue cannot be considered as neither from organic only nor PPC only.