You do not need the T model oregon. There are a lot of free maps out there. If it were me I would go with the Dakota 20 or the Oregon 300 or 450. There is also the Delorme PN-40 which is a great unit.
I have the Colorado 400T. If I got a do over, I would go with the Oregon 400T. The functionality of the Oregon/Colorado series is amazing and well worth it. What you get for the extra cash is true paperless caching with your cache info on the unit, WhereIGo ability, and the ability to beam cache coords and wpt coords to other users.
Also, if you get the Oregon, dont cheat yourself and get one without the terrain maps. 400T is the way to go. Just yesterday, doing a cache in a god awful place, courtesy of mathman and OPS, I was able to use the terrain function to figure out a slightly better path out of the worse marsh on the face of the earth. You wont use the terrain maps for every cache, but when you do need it, you will be very happy that you have it.
You can get free topo maps or save a little money and get the DVD. I just ordered the Oregon 450 and bout the DVD for 24K Northest Topo. $93. You can use it on as many units and it has auto routing.