It depends on your budget as usual. There are probably hundreds of ways to get followers on IG as its been a hot niche for years and there are plenty of creative and not so creative providers and ways to attract new followers. Cheapest will definately be a panel - pure numbers and useless in general. If you want targeted followers you can try follow/unfollow, story intereactions or a combination or both. Paid ads (target non tier 1contries for lower cost) mass Dms, shoutouts/giveaways fom same niche accounts, mother/slave etc etc. Whatever you do content will always be the key if you want to be sucessful so I would suggest that you mark all checks there first and the growth will come. Will be happy to chat more on this if you need help or specifics.