My solution is simple...
Do Not Boost this.*** Spoiler - click to reveal ***After collecting all the collectibles,
For me it was Ectors statue, you recieve 30,000 gold. By this time you will have used 10,000 or more upgrading and making your way through the game. Spend as much as you can in the shops, and if you get stuck with only 28,000 item to buy but not enough, just go buy focus points from the old hag.
If you are completing the game dont waste your time with the other solutions.