The iPad is a single user system. I think the simplest solution is to buy the $325 iPad for others to use. Be sure to keeps the receipts for all iDevices.
edit: Guided access may be what you are looking for. It allows you to temporarially lock the device to one app. You need to enter a password to get out of guided access. Download some other web browser. Lock the device to that web browser.
To start Guided Access:
Launch the Settings App.
Go to General and choose Accessibility.
Turn Guided Access On.
Set a passcode.
Launch the app you want lock the device into.
Triple-click the Home button.
You can choose to disable touch or motion in addition to disabling the Home and volume buttons.
Tap the Start button.
You could do all your working in one of these all-in-one apps.
All in one Applications that emphasize security
Good Collaboration Suite
"Secure mobile app-to-app collaboration.
The Good Collaboration Suite includes Good for Enterprise, Good Share and Good Connect secure mobile apps, simplifying access to email, calendar, contacts, tasks, instant messaging, browsing and document sharing. These apps are built using Good’s next-gen containerization that includes secure data sharing between any Good secured app as well as app-level encryption independent of the device used."
Quip -- General all-in-on App
"Quip is a modern word processor that enables you to create beautiful documents on any device, including the iPad, iPhone, and the desktop. It combines documents and messages into a single chat-like “thread” of updates — making collaboration easy."
" content administrators can proactively push important content to a user's device. All content is securely stored, synchronized and available for offline viewing."