a place where I can sing without anyone hearing me? (10points!)?

I love singing.
i sing really powerful songs such as listen by beyonce, or bound to
you by christina aguilera.
I have an upcoming event for singing next week, and i want to do
really well, but i can't practice without constantly worrying about if
anyone can hear me outside the house!!!
obviously the house isn't soundproof, so if you yell a little bit, you
could hear my voice from outside, and i think that's a little
embarrassing...

I tried the basement, but there are little windows around the entire
basement,... my neighbors come out to their backyards a lot, so it
makes me think they'd hear me there too. i tried closing all doors of
the rooms upstairs, but then i'd think they'd hear me through the
front door that is right beneath. i would not like to try the bathroom
- singing while in the shower because first of all, you're wasting
water, second of all, you can't even properly practice, and lastly,
people outside can still hear you loud and clear- it's just yourself
that you can't hear. i wouldn't want to go outside to the park because
there's always someone there. i didn't try the garage, but would
people not hear me?

and, i even tried researching about soundproofing a room, but not only
can we not afford the amount of money to be spent to make a sound
proof room, but we can't afford the time to make a sound proof
room......

please help...