Step 1 - message Joe
Step 2 - buy and wait
Step 3 - enjoy your new Glasscages tank!
Seriously, for a 300g and that budget, just go custom and get what you want. Call a few custom tank manufacturers and get some quotes.
I'm around $7k for my tank and stand. It's in my build thread. I could have gone a little cheaper on the stand but went with Chris Benner and his aluminum stands. I could have also gone slightly cheaper on the tank but got almost every option Joe offers.
Speaking of, Joe never once sold me anything. Never tried to upsell or push me in any direction. I was all over the place early on too.