I changed out my inverter pump a few months ago. You are correct that it is just in front of the passenger front wheel. I am not normally one to try and do these types of jobs on my own, but I thought I'd give this one a go. So, I'm sure if I can do it, you probably can too. You'll just want to set a few hours aside to do the job. It actually sounds harder than it is. You will need to take off the front grill and the wraparound bumper to access it. Not as difficult as it may sound. Then you will be able to look up through the front passenger wheelwell and see the pump. I think one or two of the bolts were a bit awkward to get to, but that's about all. You should be able to look at it and see how it all connects up. Unfortunately, I didn't take any pictures.
Here is a link to a diagram that shown how everything fits together. The pump is in the bottom righthand corner of the diagram:
http://jp-carparts.com/toyota/partlist.php?maker=toyota&type=715110&cartype=2&fig=8432
Having said all that, it shouldn't be a difficult job for any mechanic, so you may just want to go that route. They could easily put it up on a lift and do it in less than an hour I would think.