Hi
The AR20 is a good rifle to start with, as long as it's been looked after there are no real pitfalls, we have a couple in our club that have been passed on over time as shooters develop, I've not yet had to repair one or even know of one that has needed repair, Target shooters tend to be very meticulous with their equipment so finding a good one shouldn't be to difficult.,
other options would be the Walther LG range for a bit more money, I've also shot a Tau Mk300 and found it to be a very good rifle for the money, other than that the PCP range is fairly limited at entry level for "proper" target rifles, There are the Air Arms S200/S400 in target variants but they lack a true match trigger and the adjust-ability or the AR & LG, Others may have options I've not thought of,
atb
Nige