Looked up a YouTube 1CC to see how close I was and saw something that's essentially a cheat with score/money I didn't know about before (and didn't use in my runs):
Finally, there exists ways to cheat the shop in this game. You can essentially "steal" items without lowering from your cash total, but this is only possible using autofire. All scores above 2.4 million used this tactic; It adds considerably more potential to your score because you get a end of level "credit" for not using all your purchased weapons.
I was able to reproduce that twice on Capcom Arcade Stadium. Not sure how to do it consistently. I was only able to buy the sub-weapon in stage 1 and keep the cash. I wonder if you can use it in later stages to buy the sub-weapon and fuel/shields.
I can’t play this game at night anymore because it gets my mind going and then I can’t sleep. I’m definitely going to attempt to do a 1 cc now that I’ve come so close but I might do what I did last time and try to get it in the final days of the month.