If my rent was doubled, is this legal?

1) If you have a written lease, the landlord can only increase rent either when the lease itself provides for an increase, or at the end of the lease term.

2) If you have an oral lease, then the landlord may increase rent on 30 days notice.

3) There are no limitations or restrictions, other than any which may be in the lease itself, as to what rent a landlord may charge for a commercial premises, or by what amount the landlord may raise it.

4) If the building is foreclosed upon, you could be evicted quickly (as a practial matter, it usually takes somewhat longer than 30 days); the protections that the federal and many state governments provide for renters in foreclosed properties apply to residential rentals, not commercial.

5) Note, however, that nothing stops you from negotiating with the bank or whomever buys the property in foreclosure--they may be glad of an in-place tenant and the cash flow therefrom.