There`s no single right answer for such a general question, except one that`s always applicable: never pay any upfront against a promise of marketing your idea to so called manufacturers. What to be done depends on how deep your pocket is, how smart you are, how much of a breakthru the idea is, etc...
Ideas are dime a dozen. I can personally say I may currently have about 10-20, some were already prototyped, many patents issued. One should focus on only one with the highest potential. Sure, during slack time (waiting for new spin of prototype for invention #1) I work on a fun stuff that can possibly make money, see
T-RexElec
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