How could I have avoided this? Am I making the right decision? (Code C1391)

Hello,

I have a 2010 Gen III Prius and I have the Code C1391 issue and I'm pretty devastated right now. This isn't new, I've known about it since I got it in October 2020 and it was able to drive it around fine until recently I had the brakes replaced (new pads/rotors). Now the car has a constant beeping and almost no brake pressure. But let's roll back to when I first got the car. I was previously driving a Ford Crown Victoria and delivered food full time. Since the Prius got way better gas mileage I figured this would be a good investment and it was, especially with the rising gas prices. Before I got it no lights were on to indicate it had issues and I even took it to a mechanic and he pointed out a small oil leak and a couple other small inexpensive issues so I bought it for about $5,500 (still have $1,700 left on the loan) with 150,000 miles. Yes it was making a couple noises but I never owned a Prius before so I thought these noises were normal. It wasn't until the next day that the lights came on but by that time it was too late. I took it to the dealer and they said the ABS pump would need to be replaced for about $1,700 (didn't do the service). However though my various online research I estimate it will be closer to $3,500 since they have to replace the brake booster too. Again I drove it around fine for over a year and a half until I had major work done at a mechanic shop (not a Toyota dealer) where they replaced the rotors, brake pads, struts and other parts for $2,600. I knew this wouldn't fix the brake booster issue but I thought I would be fine without addressing that. Then the car started the constant beeping with no brake pressure as I mentioned earlier. I'm not sure how I could have avoided this whole ordeal. I guess one way would have been to get a newer vehicle because through later research I saw it could have been covered under warranty but the car is too old and mileage is too high to claim anything. Before I got it I considered taking it to a Toyota dealer to get looked at but I'm not sure if they do that service and I was also worried that even if they do they might try to lie to me so I buy one of their new vehicles. So I'm not really sure how to proceed here. I considered cutting my losses and just get a newer Prius but I'd be paying more than $3,500 for that and I already paid so much for the new brakes and struts. My current plan is to take it to my local Toyota dealer, bite the bullet and pay the full cost to fix it. I've looked at various videos and there's no way I can do this service myself. This is just a hard lesson learned. Any advice on how to avoid this in the future and/or how I should proceed? Thanks!