The GasGas TXT125 is too small in my opinion. It will be difficult to get the torque to launch you up obstacles. It is really meant for junior/schoolboy class.
I used to own a 2001 GasGas TXT280 and it was excellent from beginning to expert riders. The TXT280 from 2000 to 2002 were basically the same bike. The Pro280 first came out in 2003 and some minor clutch issues if I recall correctly. All later years are flawless. If you can find a 2000-2002 TXT280 for a good price, I would highly recommend it as a starter bike. If trials turns out to be your thing, then you can always upgrade to a later model.
Trials bike hold their value fairly well compared to our enduro bikes. I haven't checked prices lately but I would guess the 2000-2003 bikes go for the $1500-$2000 range.
EDIT: I just noticed you are in Tennessee. I would call the Trials Training Center (located in TN). Dan Brown (the owner) may have some good used bikes for sale.
http://trialstrainingcenter.com/
Also, if you didn't know yet, their site has some great how-to articles/videos. They are good for enduro riders too.
http://trialstrainingcenter.com/how-...rcycle-trials/