That's the thing for me too: I don't want to pay for the agent's mistakes, even if those mistakes are in part the fault of my prompt. I'm fine with having usage limits if it means I pay a fixed cost per month. Not sure how long this will last, considering how expensive all this is for the companies to run, though.
I feel like Amp's costs are actually in line with Sourcegraph's costs, and eventually Anthropic, OpenAI, et al. will all be charging a lot more than they are now.
It's the classic play to entice people to something for low cost, and then later ramp it up once they're hooked. Right now they can afford to burn VC money, but that won't last forever.