Depends where you are in the world. Any local shops may offer you a discount on a multiple order. Or shop around mail order, many suppliers offer reduced prices for 10 or 100 films.....the internet is your friend in this case.
ou can buy 120 films in bulk, in ten or 20 roll packs, or perhaps larger packs, but most 120 comes in singles or 5 packs, so your best option is to look for singles in multiples and 5 packs in multiples .
120 is not sold in 100 foot rolls, because it needs its paper backing. They used to sell 70mm long rolls and some medium format cameras, like Hasselblad and Mamiya RB-67, could be fitted with special long-roll 70mm backs to take it. High volume portrait studios often used it. I don't think the film is made anymore, because the 70mm Hasselblad backs in EX condition often go for less than $50 while 120 backs cost 3 times that.
Fine Art Photography of Indiana and other places no one else photographs.
I have cut and slit bulk 70mm narrower so as to allow reloading of previously used 120 spools and backing paper.
It can save you cash if the 70mm roll is the right price, but it is also a big PIA.
It is no longer worth it to me , having tried this route re-loading 20 rolls.
I now use the bulk 70mm in a modified polariod J66 to shoot C-41 Portra negs that end up 70mm wide x 4" long per exposure.
Modifying a Paterson reel to load a 5' long piece of 70mm is the PIA of this approach though.