Facebook Vs Instagram: Ultra targeted Ads

I need to spend very little on ultra targeted adverts. I have one spot left on my yoga retreat.

Need it filled to get some profit.

I need to get through to foreign yoga lovers who are already in Vietnam.
Ultimately, I need them to go and buy a holiday.

Which would be best? Anybody who can do this for me? Small budget but also small amount of time?

Hi,
what's your budget?
What do you need to conversion to come in at?
How much does your retreat cost?
Do you have a link to your website?
How will you close the lead/potential customer (do you accept payment via your website or ... ) ?