Go to the Backcountry Gear website and search "tarp." You'll get a wide variety of flat tarps, shaped tarps, poncho/tarps, and materials you can compare - including sale prices on a few of them.

Generally, you'll get what you pay for. One thing to be aware of is that a groundcloth typically will not have grommets or tie-downs along the edges to which you can attach guy lines. You can add these (though they may easily rip out if not reinforced), or improvise attachments using small rounded rocks, but it's a lot less conveninet.

If I were to go back to a tarp, it would probably be the MSR Twing (or a similar shaped tarp with one closed end, like the Integral Designs SilShelter); however, if I wanted a "flat" tarp, my choice would be the Granite Gear White Lightnin' (which is currently on sale at Backcountry Gear.)

So why don't I use a tarp? Because solo tents have become widely available, and weigh the same or less (remember, tarp camping also requires a groundcloth.) The tents are just more convenient and weatherproof for less weight, so I'm willing to spend the extra money for a tent. I tarp-camped for a lot of years, when solo tents weren't available and two person tents weighed six pounds, and found it delightful (except for the bugs), so I'm not trying to discourage you - but just be aware that this is one area where it may pay to spend more.