Went to the range yesterday and shot my first build, which is pretty much a RRA Entry Tactical.  First five rounds hit about 5 inches high and to the left @ 100 yards with iron sights.  It was a pain in the ass to have to walk out to the target every time to check it out after firing.  What is a decent inexpensive sighting scope that can be used at 50-100 yards in order to sight in my rifle?

check out burris

+1 - A buddy and I didn't want to spend the big bucks, so we went halves on  ONE OF THESE.  It's a little bulky, but the price was reasonable, and I can easily see .22 holes at 200 yards.  Good glass for the money, IMO.  My only minor gripe is the eye relief (or lack thereof) when wearing shooting glasses––my glasses sometimes bump into the ocular.  

ETA, I've found some good optics deals on SWAA's sample list and Natchess.

Got a Barska for like 60 bucks from sportsmans guide.  Not much eye relief either but I don't think spotting scopes really have much generally.  It works great and has a clear picture.  20x-60x  Can see .223 holes easily up to about 300yds.