I'd recommend you get ahold of a magnifier and think out the amount of space it'll occupy on your gun combined with the red dot. It can turn into a heavy, bulky, cluttered mess.
I have one of the Primary Arms 3X maginifers that came free with an EoTech I bought. Never even considered installing it when saw how much real estate such a contraption would occupy.
How much magnification do you want? For $120-180 you can get into a Vortex Strikefire or Sparc. Both come with screw-in 2X magnifiers. They aren't great, but they're functional. The Vortex scopes themselves are excellent quality for the price, however.
For more magnification on a budget, I'd look at a traditional scope...Nikon's ProStaff series is pretty solid for $150 or so.
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