I think the fastest and reliable, but definitely not the cheapest way, would be a document scanner like a Fujitsu IX something. you'd basically cut all the pages so that they're a format the scanner can accept, stuff then all in there and hit scan. A few seconds later you have a pdf. Using a flatbed scanner is probably the slowest approach, but the one with the highest quality. The cheapest way would be taking photos with your mobile, there are frames that you can buy (or make yourself) where you put your phone in on the top and then place the page below, so that you'll get a consistent quality. light can get tricky with these.
ebay? https://www.ebay.de/itm/363032999659