Most places will charge more for the hex receiver. It seems to be the more desired configuration by collectors, as it was largely phased out by 1935/1936. So they tend to be older. M44 variants (the shorter carbine version) are getting more and more rare now, and will be more expensive. Most people consider a Finnish Mosin Nagant to be the pinnacle due to the Finns having such high standards for manufacturing and accuracy.
As far as scopes go, unless you pick up a rifle that is already drilled and tapped for a scope (which stores will charge a lot for, around $400-$500), you will have to drill and tap it yourself. The receiver shape doesn't make it any easier or harder- the scope was side-mounted (like an AK-47 typically has to be done), so it doesn't rest on the receiver.
There were particular rifles marked for sniper use and then the holes were filled during arsenal refinishing, if you get one you can see the closed holes in the walls of the receiver. These rifles tend to be more accurate (stronger rifling, etc).
You can figure out all of this stuff based on the markings stamped into the wood and the metal on the gun. There are hundreds of markings, and only some of them have a known meaning.
This site has a great wealth of knowledge on those markings and the history of the Mosin Nagant: 7.62x54r.net
There are a few sites that you can buy from that will charge you $10 or so for a "hand pick", meaning instead of grabbing the first one on the rack they will hunt around a bit for a good one for you- something with strong rifling, good wood condition, etc.
I purchased a hex receiver 91/30 from impactguns.com and ended up with a very nice Tula made in 1936, with ex-sniper markings. My stock however had been replaced somewhere along the lines by the Ukranians (which I can tell due to having a Ukranian refurbishment stamp on the buttstock). Serial numbers all match except for the magazine floorplate (which must have been force-matched during refurb in Ukraine).
I could go on- but that's now what you came here for
. Just gives you an idea of the fun/history you can get for $100