Commercial Ticket Endeavor

I am currently IFR and have been giving some consideration into going
after the commercial rating. I have been studying the requirements and
wanted to post some questions to the group...

Please bear in mind that I don't typically cut corners when it comes to
safety, but am always looking to save a few $$$ where it makes sense.
After all, this hobby/passion is expensive enough as it is! (I
currently own a 172 and it's all I can do to cover the annual expenses
on it and still have enough left over to put gas in it from time to
time)

My bottom-line question is... How much is this going to cost me and
can I really afford it?

Aside from the 10 hours of complex time (plus the checkride in a
complex airplane) and the instructor costs for those 10 hours, it seems
like most of the requirements may have already been covered in the
instrument training or can be done on your own. For example: The 300
NM XCtry, 5 hr. night-VFR with 10 to's and lndgs. at a towered airport,
....

I know there are some new maneuvers, but those can be learned in the
172 and confirmed in the complex plane as part of the 10 hours.

It just seems to me that most of the requirements may have been met
during previous training and/or by getting out and flying?

Is it reasonable to think that I might be able to:
* Spend 4 or 5 hours in the 172, learning all the new maneuvers for
the checkride (at the cost of fuel and an instructor)
* Spend 10 hours in a complex plane (at the cost of the plane and
instructor), learning the plane and dialing in the maneuvers
* Take the checkride (cost of DE and plane)

If I flew a 2 hr. day XCtry and 2 hr. night XCtry, meeting the NM
requirements, with an instructor while working on the instrument
rating, would that carry-over? Is the requirement that a logbook entry
exist for those elements, or that they were done while training for the
commercial rating?

My ultimate goal is to get the CFI ticket, and let other help support
my habit! ;-)

I'm interested in hearing thoughts or experiences from others.

Best Regards,
Todd