I've got a DSA carbine length and would like a 1-4 with some good clarity. I've read the viper 1-4 pst is great and would like to keep it under 600 with the mount and rings.
Personally...I'm not one for mounting optics on FALs, but I have a friend with a DSA Para Carbine that uses the DSA mount linked below with a Burris MTAC 1-4x and it does very well. He's had it for a while now and never experienced any issues with the mount becoming loose or otherwise losing his zero on the scope. I think he got his mount and the scope for <$500 IIRC from what he told me when I helped him install the mount (but the MTAC is certainly a cheaper optic than the Viper PST).
If you get in touch with Scott at Liberty Optics or Doug at CameralandNY (both Hide vendors), you should be able to get the best pricing possible on the optic and then get your rail mount and be in and done for well under your $600 max budget.