Don't worry about the stands, there are actually only 2 chest exercises to use them for, chest presses and incline chest presses. You can also use them with a bar to sub pull ups, but the tubing works fine. I bought safety stands (the Valor has been out of stock) and because my barbell is short and my bench too high, I can't even use them for incline work. Anyway, you may just need to lighten your barbell a few pounds for flat and incline presses, but you will still get great results, it's only 2 of the exercises in the chest discs anyway. And in meso 3 you can do the plyo leg workouts so you won't even need squat stands or a weighted vest.
I will say the following are really necessary, at least for meso 1 and 2, I have not looked at 3 yet (I like to be surprised
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Resistance band - this is a must, but you can buy 1 in a sporting goods store for around $12, you can use any brand, just make sure it's at least 6 ft. long, the shorter ones, I've heard, end up being difficult if not impossible to use for many exercises.
Burst resistant stability ball - Cathe's are $23, I know Amazon has other brands so you can get free shipping on them. But they are all generally around $18-23. Make sure to get one that is "burst resistant".
Tubing with over the door attachment - About $15, Cathe's come with the over the door attachment. I don't know of others that do. This would be used to substitute pull ups if you don't have a pull up bar.
You have a step, so I don't believe you have to have the mini step too.
I'm assuming you have dumbbells, maybe barbells. If you don't have barbells, I've heard you can just use your dumbbells instead.
Soooo, with all that said, you are gonna love STS, don't worry about the small stuff, it's a great program, and a couple of tweaks won't change that. Let us know how you like it when you start!