$1600 for the same old swingarm - forget it! Any competent metalwork / aluminium machineshop should be able to build that worn area back up with welds, machine it down flat, then polish it up. Failing that (metal left too thin to weld) they can cut out that small section and replace it, machine and polish it - good as new.
Done properly you shouldn't be able to tell (ask around who's good - welding is an art and some ain't so artistic!). Maybe get them to polish the whole swingarm, it'll look a million $. Failing that for 2nd hand ones try;
Yes the all the 900 injected swingarms should fit. (1998-2002) and as the 1000DS swingarm is specified as an upgrade for 900 SS ies by DP that should fit also. (Very sweet swingarms those). Failing that a UK outfit makes their own design alloy swingarms for injected SS's.
Have fun with it!
Do I laugh at Harleys? Hell no - I respect anyone who can sail a boat on 2 wheels.
2005 Red 999 Bip / Mono - Termi, Ohlins steering damper, DP CF hugger, Clutch slave and Ti Res caps, Evo fender eliminator.