From what I have read, yes it is advisable to keep at least one hide in with a snake in a rack, although some people use thin sheets of paper that they can hide under. Personally I would keep a hide though.
As for a rack for 10 snakes, you can get one here for four snakes at £40, which is pretty cheap but if you specifically need it for 10 snakes and space is limited, maybe a bigger rack will help: https://www.internetreptile.com/reptile-racking-systems/5689-vivexotic-snake-stax-stacking-system-beech-reptile-racking.html?gclid=Cj0KEQiA5bvEBRCM6vypnc7QgMkBEiQAUZftQOhm3QeQ2e3yNHT3zb6w29ZkF kGpuzdMYe6yKUhsndYaAjsE8P8HAQ
Alternatively, websites like this allow people to advertise second hand racks, you might find something cheaper there: http://www.preloved.co.uk/classified.../reptile+racks
Finally, making your rack is not impossible and converting a backless bookcase is always a good idea for a cheap rack: http://www.argos.co.uk/product/9063983. Although you would have to check the sizing between shelves and the width and length space for accuracy, you could buy and use your own 64L RUBs on the shelves and put the heat mats underneath them. If you google 'backless bookcase' there is a bunch of bookshelves that could be placed back against the wall and have the wires for heatmats coming out of them.
Whatever decision you choose, good luck and I hope your snakes like their new home!
