I own every rifle on your list (several times over) and most of the other ones mentioned in this thread.
First, I will answer your question directly:
1. The most accurate will probably be the M-48, IF you get the right ammo for it (198gr bullet).
2. Best budget ammo is 8mm (the Romanian stuff is fantastic), but the 7.62x54r is real close. There are some great deals on it right now.
3. M-48 has an intermediate action, so while it IS a 98, it is not a full lengh. Ultimately it is probably the best if your ammo explodes, but I wouldn't screw with it (ie don't build an elephant gun from it).
4. Price wise you can't beat an M44. Like new ones are 50 bucks. Sure, you can get a M91/30 cheaper but it will be beat to pieces.
If those 4 are your only choices: I'm a Mauser guy but I don't like M48s, so If I was you I'd get the M44.
All that said, I have to agree with some other posters in that I have some other suggestions. Consider:
M39: Mosin action, better stock, Hbar, better sights, cheap to shoot, wicked accurate!
Swede 96: also one of the most accurate milsurps you will find. Nice shooting, but costs a lot to shoot. No more 6.5x55 surplus. :(
Yugo K98: one of my personal favorites. Real Nazi German K98 refurbed to VG-EX condition by Yugoslavia. Identified by commie crest on receiver ring and Preduzce 44 on siderail. Shoots 8mm, has history. Nice weapon for $125 or so.
Finally, Russian and Romanian SKS are C&R if you want a semi. Share ammo with your Kalashnikov. I have a excellent Russian for sale if anyone is interested, $260 shipped.
Hope this helps, email me if you want anymore info on anything C&R.