If the first film is only based on The Gunslinger, it wouldn't need a huge budget. Most of that story is just Roland and Jake walking through the desert. What concerns me though is that The Gunslinger (IMO) is kind of a terrible way to introduce the series on film. It's very slow, very strange and not a whole lot happens. It's probably the most "western" of the books (other than Wizard and Glass), and westerns haven't exactly been kicking ass at the box office lately. And while you could argue that doesn't matter, I would say it does if you want to see this series completed on the big screen. I feel like The Drawing of the Three is the most engaging of the stories because it introduces Eddie and Susannah and because it takes place in both worlds. I don't know. Maybe they could kind of combine The Gunslinger and TDOTT?