the arc ls2 has alot of different variations and can be found from anywhere to $700 to $1300 depending on the version.
it is a very good preamp, even by todays standards. the arc ls 15, 16 and 16 mkii are very good also. the ls16 mkii is the best of the bunch and cost the most (imo).
points to consider....
the real strength of the ls2 is that it only requires 1 tube, hence tube rolling is cheap and easy.
the ls16mkii takes 2 "super tubes" hence there is less tube rolling but a cheap consistent source of tubes. the ls16 mkii is a very high resolution design.
balanced or unbalanced..... the ls2 is not a true dual differential design. the 15 and 16 are. if you are running balanced, then i would strongly recc. looking at the newer 15, 16.
remote control - are available on all three. the arc ls2b mkiii (the mk iii is a pretty rare pre- the last of the 2 series)has a remote control, something to consider. to remote or not to remote.
what is your price range and taste ?
the arc preamnps have changed their sonic signature as time as progressed. their sonic signature may not be to your liking, so audtion the different series if you can.
also, another pre to consider is the pse hl-1. it is a hybrid design with remote, ht bybass, and balanced. requires only 2 tubes. pretty rare on the used market and is better than the arc pre's even costing up to $7500. it is very transparent, dynamic and delicate, and very musical. pse is located by magnapan and audio research in minn. very small operation that has been around a long time. his gear is very reasonably priced at $2500 - $3000(NEW)/ $1000 to $1500 used) and has a long standing reputation of performing to the level of gear on the $5k to $7.5k range ( 2 to 3 times more).
good luck,
mike