I have been looking for another 100 for a while now.
Your best bet is an 03 or newer. I have an 01, love it but the 5 speed in the 03-07, side airbags, are better all around. And if you mod the 100, you will lose fuel economy, so best to start with an 03 up.
Mine is fully moded, with drawer and fridge always in, just checked mileage yesterday 12 city, so not too bad. Will check highway mileage next week.
They are not that rare, but finding one that fits your liking could be. They are going to be super rare after 07, with less than 2000 sold in the U.S. per year after 2008.
Cars.com is the best right now. Cargurus used to be good but less rigs on their lately. Autotrader ok. CL ok but usually if they are on Cars.com, they are also on CL.
03s are coming way down in price 14-18 depending on mileage. 04-06s are 18-27k depending on mileage. 08s are 35-45 depending in mileage, also these are 200 series.
If Lexus is your cup of choice, add about 4k to the prices above.
I am no expert on these but I seem to know more than any sales guy I have talked to in the last week.
Also what do you want to do with the truck? These are great for family wheeling trips. Very capable but I am not convinced the limited travel of the torsion bar is equivalent to the newer gen IFS or Solid front axel options available.
Hope this helps.