to get into the 50-100 a month and the packs i referenced, you need to understand gear in L2 a little better:
that rare accessory pack costs 25 bucks a month. It contains Blessed Valakas Necklace, Lindvior Earring, Blessed Antharas Earring, Tauti Ring, Earth Wyrm Ring and a CoC belt. To put those into perspective, B Vala is 65 Bil to buy on market, Lindvior is also 65 bil, Blessed Anthy is around 30-40 bil, Tauti and Earth Wyrm are about 10 bil each, CoC belt is about 40-50 bil. Putting that into cash value at the NCoin rate, youre approaching well over a grand. This is why I mentioned the rare acc pack.
Why are they so expensive you might ask? Simple answer: supply and demand, plus 1-2 clans farm all the epic world bosses and control those epic jewels. They also get crushed to make god jewels. they also cant be obtained every single day because world bosses are on a cooldown. I can go into the history about how these items evolved but it doesnt really matter. The game is balanced to players having some type of epic accessories now, and thewyre always been extremely rare and limited. This is an extremely cheap upgrade and why many consider it part of their monthly expense. I recommend logging in and looking at the auction house and reading the item descriptions of what i just listed. They are pretty game changing for your character in their stats/bonuses compared to not having them.
Do you need them? maybe, maybe not. depends on what YOU want to do.
You can afk solo mobs and have little to no social interaction by spending nothing. If you want some social aspect, or to get a change of scenery in game and see stuff, you'll probably need to spend a little bit unless you dont mind xp'ing blazing swamp for months on end.
Regarding upgrading gear. you don't exactly upgrade the same weapon over and over like other games. You can upgrade R99 and R110 to Bloody/Dark and you can upgrade your R99 to R110, but its extremely expensive. People upgrade gear by crafting and enchanting. You craft by farming the mats in areas after 105. a +12 Bloody R99 weapon with mid SA's will be the same wep you use until you quit if you want it to be and its around 20-30bil depending on weapon type. You can also go the tauti weapon route, shadow weapon route, theres a handful of options all at different price points. you can also stick with the exalted wep and see how it goes, but the exalted wep is pretty bad.
Enchanting gear is the way you can upgrade, but you can break your item and have nothing as well. I'd suggest reading about enchanting before doing it. When armor sets get +8/9/10 they get additional set bonuses. For example, earlier i mentioned +8 r95 leather set gives 10% skill refresh. That set costs around 6-8 bil.
If you dont care about xp speed, drop the destiny pack and prestige. However, there are drop rate increase runes in there too, so keep that in mind since drops are important to you. Prestige rune is pretty good on the bonus it gives too. Same goes for using vitality items.
Lineage 2 is a grind game that is extremely gear driven. What is needed for you to enjoy the game is totally dependant on you and what you want out of it. You seem to like the afk minimal input setup, stated you dont mind spending a little money, and want some social stuff. This game has a lot of min/maxing in it. there are 100s of things to do to upgrade your characters.
final edit: a top limited R110 weapon +12+++ is like 160-250 bil, a dragon weapon is well over a trillion adena. what i'm listing for you isnt even remotely close to top end game gear. im trying to list the cheapest way possible for you to have fun in the game