It all depends how much you are ready to spend, if you spend a lot of money you can buy good equipment and farm with just 1 client and buffs from l2 store.
If you want to spend the least amount of $ and use 3 clients to farm solo, you will need to invest around 300-400$ for start. That is assumption that you don't want to deal with trades and that you want to have fun from start . Out of those 300-400$ you will need around 200-250$ to buy +12 Bloody weapon with 3 SA without which you wont be able to farm alone properly and maybe 50-150$ more on items to keep your little group able to survive and farm efficiently.
Don't expect to get enough adena to buy shots and materials needed for daily farm (especially since they again "adjusted" adena drop rates, at least that's my experience) until at least 105 lvl (this also depends on your gear, worse gear means you will spend more shots to kill mobs)
You can get into groups with other people but they are not that often and you will have to start them by yourself most of the time and you should expect everyone to be afk in max 10 mins after they join