So 30' x 30' is your back yard - how large is the total lot area?
One solution might be to mount a mast to the side of the house, or on the roof using tripods designed
for TV antennas, and use that to support the center of the G5RV. Then you would tie one end off
in the back yard (possibly to a mast attached to a corner of the chain link fence) and the other end
to the front yard (finding some suitable support.)
And if you don't have room for the G5RV, consider a 20m dipole, or even 20m and 40m on the same
feedpoint with coax from there to the rig.
Are you a member of the local ham club? You may be able to get a few members to come over for an
"antenna party" to help you set up an antenna, solder connections, and test the antenna out. (Its
an old tradition that doesn't seem to happen as often these days, but a great way to learn!)
If you become known as an antenna junk collector it is possible for someone to offer you a trap vertical for free.
Or enough scrap aluminum tubing from broken CB antennas that you can build your own vertical.