There are four routes to go in an AUG or AUG clone. Currently there are no new rifles being made.
First go with the classic preban Steyr A1, A2 and USR rifles. They will be used, some might be in good shape due to collecting value. They go for $4,000+
Second get a new Steyr A3 that had a Sabre Defense made receiver and parts made in Austria by Steyr. Only about 1500 made before Steyr shut down the line, and also Sabre got raided for other things not related to the AUG and was shutdown. They MSRP around $2100. Then on up.
Third get MSAR for under $1000 NIB or used could be cheaper. Bad thing, company has "moved" and yet to start any sort of production and in several law suits. Also they improved the rifle so parts from Steyr will not work on them and vice versa. Ratworx makes after market parts and tries to help fix rifles when they can. MSAR also made several generatons, each with an improvement over the last, with the final one that is called NATO stock that will take M16 magazines.
Fourth is the TPD AXR rifles, NATO Stock that took M16 mags and made with many Steyr parts. They also went out of biz for one reason or another. So no support if you find a rifle, but what I heard well made.
All this being said I am a Steyr fanboy and own the A3. Runs well, no problems out the box except magazine wear in time. MSARs had issues in all gens but had great customer support. You can shop around at this site, even Steyr turns to him if you have some questions; he stocks all gen parts for AUG.
http://www.pjs-steyraug.com/
Good luck and happy hunting.
Khest