I would personally recommend getting an authentic 91/30 sniper. I got mine a while ago and havn't regretted it. Though be forewarned that sighting in the PU scopes can be an absolute horrific job at times.
As far as if they're readily available... that's debatable. I know in the years I've been collecting I've seen two, one of which I currently own. Now, obviously they're out there. It's just a matter of finding them and then convincing the person to sell.
A repro is... an option I guess. I havn't heard of anyone making repro PU, PE, or PEM scopes and mounts though I havn't really checked that hard. Bending the existing straight bolt handle would also involve some woodworking, and I personally find them to be absolutly ugly to the nines. There is a guy in the States though that does repro sniper bolt handles, does a very good job of them at that and they sell for about USD$60. Just pop off your straight bolt handle and replace it. I seem to recall him also giving USD$10 off if you sent him your original bolt handle as well.
As far as costs go, I'd say about $150 for a good quality Nagant, and I'd recommend trying to find one of the de-commisioned, factory refinished snipers. A quick look on eBay shows up a PU scope, and the corrosponding mount for USD$200 each, so about CDN$500 there, then, depending on if you want to have a gunsmith put the scope on and cut the wood and all that, another $100 or so. So, anywhere's from $650-$750 should get you set up with a re-assembled 91/30.
Which is actually cheaper than what I find to be the going rate for original 91/30 sniper rifles. Makes me think I overpaid for mine...