Any modern computer will run flightsim X at very high to max settings with all the addons your heart desires !
However to keep the FPS at or over 25fps with these kinds of settings
I would suggest at bear min PC with at least
OS-Vista
CPU-AMD64 2.4Ghz
RAM-2g
Video card (any modern PCE with at least 256mb of ram will do just fine) Hint here...... never run flightsim with SLI always leave room to add more monitors
Remember this would be the bear min PC that will get you up to that............ o hell ya baby 25fps !! with very high settings and all the new fun stuff that goes with it:-)
So the bear min price you ask
well plan on spending about $500 (with out monitor) for a starter PC to get you up in the air with FSX
Hope that helped put a smile on your face
see its not soooooooo bad
Have fun