O365 Restrict access based on IP address... SSO options for O365?

 I need a way to restrict access to Office 365 based on the users IP address. We have regular retail workers whom do not need access from outside of our building. Microsoft's own solution requires ADFS, which we do not have. We also do not use active directory. Google Apps has an add-on which can do this, but can't find anything similar with O365.

So now I'm looking at SSO solutions. I know many of them have this functionality, but also noticed some of them requiring active directory. I would need a "cloud" based active directory option.

Any insight into cost effective solutions to accomplish this? We only have around 40 users.
Also, is there an advantage to working with an O365 reseller? Do any of them actually offer discounts?