Do you have a list of tablets that will run surveys offline?
If you are using Lighthouse Studio (formerly called SSI Web) 6, 7, or 8, then you will want to use SSI Web CAPI which runs on devices that are using Windows XP or later. Windows tablets are rapidly dropping in price from major manufacturers like Dell, Acer, etc., and are becoming comparable to Android tablets in price. For example, this link to the Microsoft Store revealed a number of affordable tablets. Of that list, $229 Dell Venue 8 Pro or $299 Lenovo Miix 2 look to be excellent choices. Microsoft Store
If you are using Lighthouse Studio 9+, and are hosting your survey on Sawtooth Software's hosting platform, then you can use the more robust Offline Surveys app on Windows and Android devices. More information about this product may be found here: http://www.sawtoothsoftware.com/offline-surveys.