Thank you! It took some work to get him there but I am very proud of the progress he's made. I've heard that remark several times before too; it's amazing how much different they can look given the right conditions!
It's sounds to me like you're free to choose a name for him then, if you want. Rigsby was not the name his original owner chose for him, but I felt like he deserved a new name to go along with his new life. Just maybe don't mention it around your roommate, if you feel that might cause issues.
Another alternative to gravel would be those marbles/rock things, the ones you see for sale in the pet stores but can find for way cheaper in craft/dollar stores. I've also seen big bags in Walmart, they're usually only a couple of dollars. That might save you a little bit, but really it's what you think would look best. You could probably also find some silk plants at those places that you could use, just so long as they don't have any metal or wires in them. Plastic is good too though, one of my bettas has both silk and plastic plants and only ever sleeps in his favorite plastic plant.
I wouldn't be surprised if he's a bit shocked/overwhelmed at first! My newest rescue still hasn't quite figured it out, but he was at the pet store in a cup for eight months so I figure it'll probably take a bit more time. It's like you said about the hammock, they just don't know what those things are at first and it takes time to get used to and figure them out. It's sad, considering how much bettas love plants and things like that, but once they do figure it out it's really cute to watch them enjoy themselves exploring!
Definitely show us pictures when you get everything set up. :)
Oh, and I just remembered- I was online shopping myself recently and Amazon has a lot of really cheap plants, both plastic and silk. It's a good place to find some decor for low prices.