Here's my SAR-1 with a Kobra (EKP-8-02, the coin cell model) on the siderail:
Closer view:
One advantage of the Kobra over a generic red dot on a siderail mount is that the Kobra's multiple reticles make close shooting easier. Any optic on a siderail mount sits quite high (the center of the lens of the Kobra is 3.8" above the bore axis, and a Wal-Mart red dot on a generic siderail mount would be at least that high). But the T-bar reticle gives you a close-in aiming point (bottom of the "T") that lets you make precise shots at 7-10 yards, while the dot and dot-chevron allow you to make precise shots at greater distances.
The dot and the top of the "T" are at the same location, so if you zero the dot at 50 yards, the dot and the top of the "T" are both dead on at 50 and 200 yards. The bottom of the "T" is right on at 7-10 yards and the POI climbs from there to the top of the "T" at 50. Or, if you foresee a mix of close and distant shooting, you can use the dot-chevron and cover the target with the chevron at close range, and use the dot for distance shooting.
I have shot numerous IPSC/USPSA style carbine matches with that setup and it works very well. IPSC targets have a little horizontal A-zone in the head area that can be really hard to hit with a high-sight-line carbine, but the Kobra makes it pretty easy.
The one caution I'd give about the Kobra is that, while it is a tough-as-nails milspec sight, if the rotary on-off switch starts getting very hard to turn due to the tight clearances, you do need to take the sideplate off and lubricate it. If you are an idiot with it (as I was) and decide to keep forcing it against increasing resistance for a couple of years instead, then yes, you can break the switch off, though you really have to work at it. If you do, it's fairly easy to fix, though.
Before I bought the Kobra, I had a POSP 4x24 scope on the siderail:
The POSP is an
excellent optic for the money (I paid around $110 for mine at the time), but it made it harder to acquire the target at close range, and I wanted the rifle to be able to serve in a HD role, so I switched to the Kobra. I can still hit well out to 200 yards with the Kobra (as far as I can shoot on my local range), but it is way faster at closer ranges.
If the Kobra is out of your reach financially, another option would be a BP-02 generic siderail mount topped by a Wal-Mart BSA or Tasco red dot. The BP-02 is the low-rise one in the center, which is the one I would use.
http://tantal.kalashnikov.guns.ru/bstmounts.html
I ordered my Kobra from Tantal, and would highly recommend him as a source. You might be able to do better than that elsewhere with a little Googling.
Either way, that mount would allow you to run a $30 BSA or $40 Tasco Propoint and stay under $100. Those sights won't be as nice or as rugged as a Kobra, but they should be fine as an interim measure. If properly adjusted, any siderail mount (Kobra, POSP, BP-02, whatever) should hold zero when removed and replaced.
Other options are the LaRue IronDot (combination red dot and rear sight that replaces the existing rear sight) and an Ultimak forward rail with a red dot, but those are much more expensive options.