I think if you're going to collect Batman, you really should collect Detective as well since they're essentially 1 and 1a. I think I might have [conservatively speaking], spent close to 20k+/- over the course of 4-5 years to complete my run. Bear in mind, I collected Batman, Brave/Bold, Detective, World's Finest, and select issues of JLA. Essentially, I collected all the Adams Batman covers as well as the interior art, and I went for both slab and raw copies, in some cases, duplicates. If you're only going for interior art, it shouldn't be too bad as there are only 32 books in total, 17 books if you only count the Detective and Batman title. The only books I completed excluded are the recent Odyssey issues from a few years back and any of the modern homages that Adams drew recently. These are not part of the original run.
Speaking for myself, I grew up with this run so it was a very fulfilling goal for me to complete it. Even more so than my Smith Conan or Miller DD runs.