The solenoid needs rebuilt- mine cost me about $2 for parts
o to
http://www.4x4wire.com/toyota/maintenance/starter/ for instructions, I only changed the one contact that had a "shelf" burned into it since the other one was a little harder to remove, Clean the Plunger and you should be good for a few more years.
I bought my replacement contact at a local motor rebuild shop, one of the ones that will rebuild your starter or alternater for you.
The second time I did this repair it took about an hour (my dad's 4runner). On the older toyotas there is an access panel thats on the inside of the wheel well that's removable (4 bolts- 10mm) that gives easy acess to the starter (also the fuel filter)
good luck