Cheap should be your last criteria for a tent. There were some serious issues with off gassing recently where tents were killing everything inside. Stick to known, name brands with an established track record. Pay the extra $ and scrimp on pizza or beer.
Dont buy cheap, I was left high and dry for around 9 months of setback and about 10K investment from a not even cheap tent, the PVC ones stay clear off.
I eventually got a foil lined tent, but the dumb thing was the tent was shipped with a PVC liner for the bottom that was toxic, got rid of that and it was sweet
I did alot of research on this, cheapest I found that WONT kill your plants is the HTG tent. Look for silver mylar lining, way too many reports of white lined tents killing plants. Dony buy into any of that ebay crap either, they all seem to have white pvc interiors.
I recently bought 2 HTG tents, and I noticed their corner pieces look EXACTLY the same as the HomeBox line but for less money. I have even found that the HTG tents have better demensions for getting a perfect 50W psf. Overall Im pretty happy with my HTG tent and plan on buying another bigger one soon.
I've built my own tents a few times using pandafilm (which may in fact offgass but I'm not aware of any issues from using it all the freaking time).
Just knock up a frame of 2x2's with some corner braces and cover in pandafilm. Apply a few construction zippers and bam, you've got a door. You can frame in vents, etc. Any opening/etc you need.
I've done everything from 125w CF to 4000w of HID's in a setup like this.