The quality content I would recommend writing yourself if you don't have any budget to hire someone. If you are worried about time look into ai writers but always use it as a way to save time instead of just replacing it. The quality ones still work IMO as long as you read and edit 60%+ yourself.
When it comes to backlinks, this is where most of your budget will go. Of course, you can get natural free quality links, but you're mostly going to be paying if you want quality guest posts and niche edits.