If not trashed, $600 is sadly a fair price. When newly imported in to Canada they went for $350-600 and now since the supply has dried up the prices have crept up into the $600-650 range. The odd rifle comes up used and sometimes still unfired for those lower prices, but they sell very fast.
For summary of each maker/code:
http://www.ycgg.org/ycgg_ww2german_pdf.htm
More info:
http://www.mausershooters.org/k98k/K98_manuc.html
http://home.scarlet.be/p.colmant/k98kmarkings.htm
For the purist view, go to
www.k98kforum.com however many members don't hold RC's in high regard. However, as a Canadian collector they are a great way to get an example of a WWII K98 that probably saw service on the Eastern Front. The site is the leading site for K98 research and publication, setting a new Gold Standard and improvement over Law's books on the same rifle.
The barrels/recievers generally match on these rifles and many bores are good to excellent. The remainder of the parts will be mis-matched with different serial numbers and waffen amts. Usually the Russians used early milled vs stamped parts (slightly higher quality). However, the Russians did electro pencil all parts to match. The stocks are also shelaced.
If in all original RC condition I would consider keeping it that way. Many RC's were 'restored' after import (Blueing removed from the butt plate/take down disc, shelac removed, repro cleaning rods/screws/sight hoods added, etc). These restorations did make them look more like a WWII German issued K98, but then again the RC variation was altered, making non-altered rifles an even rarer and historical variation.
Some individuals would pay a premium for single rune rifles, rare maker codes (S/42, BSW, BNZ44, or late war Kreigsmodel Codes), or former snipers (some still have the zf41 rail) or a thick walled LSR drilled reciever. In the end, most RC's are worth the sum of parts - which would come close to $600 and if an ex-sniper probably closer to $800+.
I hope this helps.