I've watched the movies and most of Star-Wars The Clone-Wars TV series, and I keep seeing battles that consist of hundreds of thousands if not millions of droids, and that started making me wonder, how much does one B-1 and B-2 battle droid cost?
If you consult the Role Playing Game books by George Lucas as single B1 battle droid cost 1,800 credit so you could say the army is expensive but easy to repair.
So if memory is correct I think B2 battle droid were 3,000 credits. The one that cost the most was the droideca they were 21,000 credits so they were less on battlefield only for protection or used against jedi.
Single suit for clone trooper was 8,000 credits that's not including training, and growing clone. I think the republic spent more money on the clones the the separatist could have spent on droid army.
Shoot troop it stays gone. Shoot a droid and its sent to repair place or smelted for ore again to be rebuilt.
Hope this helps. If you need more info consult George Lucas game books smuggler version it gives prices on droids and ships. There is another version for clones.