i too wanted to give trials riding a go.
although i am not familar with that gasgas model, i remember reading that they are practically bulletproof.
another common theme was that the bike and their differences are not as noticeable from model to model as an enduro.
my friend and i both got the same bike at the same time [2001 gasgas txt280] and soon had the same experience.....we are by far the weakest element in the equation of riding. it kicks our butts everytime.
i think you would be hard pressed to find a newer bike for the price you stated.
some things you may need to do on an older trials that a newer one might not need would be springs and possibly tires.
i think its a buyer market for most bikes now, and especially an older trials.
if it were me, i would try to get it so that my price with all the updates [possible springs, tires, mc, etc] is at the price you stated.
if you have to put some decent money into it, then you might as well get a newer one that doesnt need all the work.
i also dont look at buying used dirt bikes as well ....buying used dirt bikes.
i see it as changing money into another form, like some people do with gold.
its hard to climb a hill on a gold coin, but then again, its unlikely it will send you the hospital.
a word of caution, dont think that you can ride without gear like you will see on youtube.