Just bought a 2006 4 Runner with 76k miles. I need spark plugs and my gear oils to be changed. (Differentials,Transfer Case)

What is a good dealer price for these services?

Not sure about the fluids, but Toyota quoted me 250 for the plugs. Bought them for the dealership for $6 each and installed myself in about an hour. Highly recommend doing the plugs yourself.

I saw the subject and my first thought was "Wait, it's not April 1st".... no such thing sir, no such thing.

Seriously though, as eluded to all the maintenance you're contemplating is easily performed with comparable or better parts for way way way less than what the dealer will charge.

differentials, transfer case, and driveshaft service
spark plugs

Even if you have to buy the tools it's still cheaper by a lot! some helpful links for you to read (you don't need ramps, I've done it without ramps)

Changing Differential & Transfer Case Fluids - Pics Included
Driveline Service - Toyota 120 Platforms Forum
4.0 v6 1gr-fe detailed spark plug change instructions - Toyota 120 Platforms Forum

mobil1, grease gun, plugs and crush washers (only thing I buy from the dealer) will run you about 100-150 depending on if you can find stuff on sale... check for mobil1 at walmart, I get my at advance auto with one of their constantly running promos...

all kidding aside if you decide to do it yourself then I'd also change the serpentine belt (if it's the original) while you're under the hood, get some MAF sensor cleaner and clean that off and get some throttle body cleaner and clean your entire intake air track... all this stuff is just nuts and bolts, it's not rocket science, trust me, you're more than capable. I recently showed my wife how to change the serpentine belt on her 4Runner and her response was "That was way to ****ing easy! I could do that!"... I love my wife but she is not what I would call mechanically inclined at all...

I agree with the others that changing your plugs out is definitely something just about anyone could do, although you have to have a little bit of sense so you don't cross thread and/or snap off a plug in there. With that being said, however, it's definitely a good way to save yourself as much as $200.

As for the gear oil, that's also something I do myself but it's a little bit on the messy side. It costs me about $80-$90 to purchase the appropriate quantity of Mobil 1 and the necessary crush washers, and after that (assuming you have a drain pan and the hand pump to refill) should take around an hour or so to complete all three. Again, you could save another $150-$200 doing this yourself.