Mark,

The main issue is that "strips of material" absorb only mid and high
frequencies, and do nothing for boominess which is often the bigger problem
in a room that small.

The cheapest sound absorbing material is rigid fiberglass, but it has to be
covered with fabric for appearance. If your budget is small and you want to
learn about treatment you can make yourself, see my Acoustics FAQ:

www.recording.org/users/acoustics

The next step up in price is foam (fireproof please), which doesn't need to
be covered but is less effective than fiberglass for a given thickness. Best
of all are pre-fab panels like my company's MiniTraps (link below), which
absorb low frequencies as well as mids and highs.

Ethan Winer
www.realtraps.com