currently, we can paginate our queries with &page=# or &before_id=# but I'm not seeing any way to know how many results we can page through before we run out.

is there any way to count the total number of posts with the tag specification we chose? in this way we could make our own page display for users of an api app even if we're using before id. something like [1]...[23][24][25]...[1024] (before_id could allow more than 750 pages I think)

if this doesn't exist, is it possible to get a total_result_count property or something?

Only the XML API currently offers this, and only if not using before_id. I tend to treat these values as being low value because they are usually values that people rely on, but they are at best, a rough estimate. They frequently change, even during normal pagination, and are cached, so you will almost always get a result that is wrong or misleading.

Even the normal on page pagination display is an estimate. It's common for people to run off the end of results as the estimates tend to run high.