Welcome to the forum!
It really depends on where you get the betta. I got a veiltail male betta from petco for about $4.99. Females tend to be cheaper in chain stores (in my experience) because a lot of people don't want to buy them.
The minimum items... that is a tough question, and prices will also vary by brand, store, etc. Here is a link to a post that may help explain it a bit better. http://www.bettafish.com/showthread.php?t=49160
In my experience, bettas barely cost anything monthly, I have seven bettas and I only need to replenish food and water conditioner once every 3-5 months!
The link above tells you quite a bit about betta care, also.
I really hope this helps, and that you can convince your parents to let you get a fishy.
It really depends on where you get the betta. I got a veiltail male betta from petco for about $4.99. Females tend to be cheaper in chain stores (in my experience) because a lot of people don't want to buy them.
The minimum items... that is a tough question, and prices will also vary by brand, store, etc. Here is a link to a post that may help explain it a bit better. http://www.bettafish.com/showthread.php?t=49160
In my experience, bettas barely cost anything monthly, I have seven bettas and I only need to replenish food and water conditioner once every 3-5 months!
The link above tells you quite a bit about betta care, also.
I really hope this helps, and that you can convince your parents to let you get a fishy.