Im currently helping Korgan recover the book of Kaza and 2 of my party members have level drain/energy drain.
What is the best/economical way to cure these?

Energy drain, if my memory does not fail me, can be cured by lesser restoration, while level drain must be cured by Restoration (or Greater version?). If you have a cleric then it will cost you nothing, but in case that you don't have one, you can either recruit some clercis to do the healing and remove them after that, or ask for help in a temple.

Ahhh ok.......Thank you.
Lots to learn in this game especially for a first time player.

It is like Levelworm say , i think it was restoration for level drain , have in mind though that when your cleric cast restoration spells , he /she gets tired right away like if 24 hours without sleep have past , sometimes i leave my guys level drained untill i am goin to make my hole group rest , there are a few spells that can protect you from energie / level drain , like for example Protection from the negative plain i think its called , if you know exactly who can drain you , from the top of my head i remember vampires and another tipe of ghost like can drain your lv , btw i hate when they drain me a lv xD , good luck and happy gaming

Energy drain will go away by itself after a while (or resting). Level drain must be cured through the use of a restoration, doesn't matter whether it's lesser, normal, or greater.

And thankfully your characters continue to gain XP when level drained even though you cannot see how much they have. (This concerned me at one point)

(Unlike say, if a characters dies and is later resurrected, they miss out on any share of XP from the battle after their death, which is not ideal)

If you know you're going up against the blood sucking Vampires, have your cleric / druid memorize multiple Negative Plane Protections, but because it has an extremely short duration, only cast one at a time on your best fighter and send him in with other buffs like haste, while everyone else hits with ranged weapons. Hit one target at a time to kill them quicker. And/or use summons as fodder. Later on you'll get a constant NPP item that helps.

It also depends on the source of the energy drain. The 9th level spell "Energy Drain" is straight-up permanent level drain, and needs to be cured through Restoration, though I'm not sure any enemies actually cast that spell. You can also usually judge by the icon: the version you get from Shadows and Spirit Trolls is a red X and is temporary attribute loss, the red-yellow V-shape is permanent level loss.

Really though, the best way is prevention. Restoration spells cause a lot of fatigue, and buying a restoration spell from a temple will fatigue EVERYONE, not just the person who was drained. I think that (Greater) Restoration will also fatigue everyone, but only if you have ToB installed (and it's a bug, it's only supposed to fatigue the caster). It also doesn't help if you cast a Restoration spell and then another vampire shows up and drains them again.

The best options for prevention are the Amulet of Power, which is available in Chapter 2, and the Mace of Disruption +2, which is available in Chapter 3 (extra shenanigans with the Temple quest required). However, you can only get them if you side with the Shadow Thieves. If you side with Bodhi, you're pretty much screwed in that department. (She claims that you'll get some magical trinkets as compensation for your gold, but you don't actually get anything.) There are a couple of weapons in ToB that have NPP, but by then there aren't many creatures that actually cause level drain, and Turn Undead will basically automatically destroy everything.

You can also use Protection from Undead scrolls, but beware! If you use them against any enemy that's supposed to talk to you (like in Bodhi's Lair or the Temple of Amaunator) you can get some really irritating glitches unless you have at least one character unprotected.

I thought you could get the Amulet of Power by killing Aran at the end of Bodhi's questline? If not, that's definitely not cool for evil parties, although it would hardly be the first time that evil parties get the short end of the stick in this game.

Oh, I'd forgotten about that. I'm still fairly sure you can't get the Mace of Disruption, though. Really though, the Aran vs. Bodhi question isn't so much about good vs. evil as it is how much of a chump you are. Siding with Bodhi makes you a chump, whether your character realizes it at the time or not. Evil characters are free to side with Aran, and good characters are free to side with Bodhi (though Keldorn and Mazzy get really mad if you side with her). I sided with Bodhi once on an Undead Hunter paladin kit once just for the lulz. I even got Keldorn and Mazzy in on it, I just had to park them elsewhere until after I accepted her offer.

I'm pretty sure the mace is in the same place whether you side with Bodhi or Aran - if you side with Bodhi you can just walk in and pick it up.

So where is the best place to purchsae a restoration scroll?