I think it depends really, on how large your company is. Some companies even hire their own book keeper.
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This is pretty much the answer. When you hire bookkeepers for a large company, the pay is higher. When you outsource the bookkeeping task to virtual bookkeepers like these staff, the pay is relatively lower. Sometimes, it can even go as low as $5/hour.
I've been working from home for around 3 years now and I can somehow relate to all these benefits you mentioned. I can attest to all of them.
In as much as working from home encourages productivity, it could also do the opposite. When you don't know how to discipline yourself a major chunk of your productive time could go to waste due to distractions that could come along the way. Although we have workarounds like using a time tracking tool, the best thing you can do is to be prepared for it, be disciplined, focused and organized.
Other than this, working from home has a lot of really great advantages.
I kind of have to agree with what Southern_Lenders said above. It's not in a way discouraging you but it's one of the least to get startup funding.
However, it's still a good concept. With a good strategy, it will eventually click and will be greatly accepted.
You can also look at this list for the 2011 startups that received good funding. It will probably also help you decide in which investment to take.