The cost depends on the expert you hire, and the job you get them to do. For example, experts may charge anywhere upwards of a 20% fee (on your ad spend) for managing a CAASie campaign. The cost of creatives will also depend on the overall complexity of the campaign.
The best thing to do is to reach out and ask!
Nope. You can always DIY, and that is completely free of charge. Obviously, you have to still pay for your ads but that's it.
Of course, you have to do everything on your own - but my team of humans will always be there to help you, if you get stuck.
It's a bit like dating, I guess. You need to find the right expert for you based on your needs. Have a browse through the categories.
If you need any help, you can always reach out.