If you're looking at a 75, you might as well get a 90. Same footprint just taller, which is nice.
Just keep checking Craigslist - you have to be quick responding to get a good deal. May have to wait a while, especially if you are looking for a bow, but you should be able to pick up a 72 or 90 (with all the fixings) for $200-$250.
I hope others will chime in because I'm no expert, but my Q tank is bare bottom and empty of plants, only two rocks propped together to form a small cave. I use mine for new fish to get used to my water conditions and so I cån observe for a few days,make sure fish is not diseased or infected by parasites/ fungus. Also usefull if a fish is being bullied, not eating...or to remove agressive fish till the new ones get settled in. Thank heaven I haven't had any disease, but also used to medicate fish instead of treating your whole big tank. In my very humble opinion , every fish keeper should have a qt. I like the 29 gal size for a qt because I trust it more than a 10 to be stable and if more than a couple fish are in quarantine, they have space to swim and stay out of eachothers faces.
-skylight
My quarantine tanks are just badly decorated show tanks. They have substrate, decor, fake plants, backgrounds. It all helps the fish feel more secure. Fish stay in quarantine for at least a month.
I agree, quarantine tanks are essential for long term success in the hobby, for all the reasons mentioned above, and then some. Everyone should have at least one.
I too like 29 as a QT, especially if you are going to keep fish of any size, or if you have to grow fish out before adding them to the show tank. 20 long is an excellent size too. 10 is a nice size for small fish and for treating a fish with meds - 3x cheaper than a 29 and more convenient since most are based on a per 10 gallons scale.
I use smaller QTs for a single school, but if I have multiple species being quarantined together, I put them in a larger tank. I quarantine fish together that are going into the same tank.
All new fish are given a heat treatment for ich while in quarantine - 88 degrees for 2 weeks. This ensures that the fish are not carrying the parasites, and that my tanks are kept free of it. Not that ich is difficult to treat or anything, but I like to be proactive with their quarantine time.