This is kind of like asking how much is a car. There are lots of tanks with varying degrees of bells and whistles. The real question is how much do you want to spend. You can probably find a 150 gallon tank on craigslist for a few hundred dollars. Will it be reef ready? Does it have thick glass? Is it center braced, euro braced or rimless? You can spend thousands of dollars on a custom tank from a custom manufacturer.
Here are some questions to ask yourself:
1. Do you want a reef ready tank? Meaning do you want holes drilled in the bottom or back for drain and return?
2. Do you want centerbraced, eurobraced or rimless (google search images)?
3. Does extra clear starphire glass matter to you?
4. Are you OK with standard sizes of tanks, or would you need a custom size?
Once you decide on a budget, and answer these questions you can get a much better idea of if your budget matches your needs.
All of that said I personally like the quality/value ratio of the SC Aquarium tanks.
Hope this helps.