Nearly zero flats out there, today when you want RR you’re basically asking for a stock gun without extras such as Lage uppers, magazines, spare parts /etc that typically accompany these guns. Many guns have multiple uppers sold as a package but if you’re looking for a basement price (you shoulda’ looked 7+ years ago) you’re getting a stock gun without box at this point potentially needing refinishing. You may specifically search for an M10/9 in general as they’re sometimes priced way below market.
Some of the less desirable package deals are original (M11/9) Zytel plastic mags which are worse than cheap toilet paper and older steel gen1 Lage uppers which have merit for sure, but Lage 1-upped himself offering a Gen2 aluminum upper rendering gen1 a slight discount item. Sabre .223/556 rifle uppers at this point aren’t worth a dime (to a smart purchaser) as the company is no longer in business, clunky, and a better option (Lage) is available. There are a few Sabers for sale fishing for suckers but the new Lage .223/556 uppers have become the current rifle upper to have. Being Lage rifle uppers cost $3k by itself (as a package guys are asking Uzi money) doubtful its on your radar for a bargain purchase but just giving you a quick lesson.
One option to save is a complete m11/9 but with a STEN grip conversion which was common before metal Zmags came about. You can convert the STEN mag back to stock and use the newer z-mags being 30 or 50 rounds and readily available, but know the price to convert/effort may outweigh the value at purchase.
Good luck. :devil