It's a bit hard to give "typical" costs because it's so dependent on how you use it. The project map size (which scales with overall project size) and the number/size of relevant files are the main drivers of cost, so working in large existing codebases will be a lot more expensive than generating a new app from scratch.

Taking Plandex's codebase as an example, it's certainly not huge but is getting to be decent-sized—I just ran a count and it's at about 200k lines (mostly Go), which translates to a project map of ~43k tokens. I have a task in progress right now to add a json config file for model settings and other project settings. To get to a pretty good initial version of this feature, I first did a fair amount of back-and-forth in 'chat mode' to pin down the details (maybe 10 or so prompts) and then an implementation phase where ~15 files were updated. The cost so far is at a little under $10.