The school bus company mentioned on IPVM is gatekeeper systems. I did a quick check of the temperature and they do list 65C as the top end. Their systems are DVR/Analog types.
Regarding SSD capacity..... 1TB are coming soon (I have one in my lab) but of course they will be pricey. If one sticks with the 300-600GB size...favoring the smaller side.... the expense (in the USA) is not as wide as it used to be.
A 4CIF good quality image will generate appx 1Mbit stream. If continuous recording is used, and 7 days is how long to keep the data before it gets 'offloaded', then the system will need appx 300GB. Allowing the system to use Motion or Triggered recording will extend the number of days at that same capacity.
The higher temperature requirement means that the components used in the system MUST be higher grade...which means more expensive. If you continue to stay with bargain systems....then you will be replacing them a lot because they will fail much quicker. The same argument applies to SSDs as well. Mechanical drives do NOT like to be vibrated while they are working and do not like to be much more than 50C or else they will suffer a premature fail. SSDs have a much higher tolerance for those two metrics.