Not as expensive as a Landy one. I did mine the cheapskate way by rebuilding one with knackered bearings, cost me about £120 quid along with a new clutch at the ssame time. Alan at the aformentioned site supplied me with a gearbox to rebuild for the cost of carriage, about £20. I also did all the work myself.
I think Alan sells new gearboxes for £250-£300, then of course you'd need someone to fit it if you're not that way inclined. So the cost could spiral.
That's partly why I said don't buy the Niva. A landy will need as much if not more work and money throwing at it. Thing is a Landy will be worth money after a few years, the Niva will most likely not be.
Oh, and for laning you could do worse than join Glass: