Awkward dent position and a bit of rust

[fondsauce]

Pics: https://imgur.com/a/CcoCfp7
Hey all, I am a fairly new driver and would appreciate some advice on this.
I have gotten a dent 2 weeks back near the tailgate. The bodyshop people reckoned it could have been a rubber mallet or something similar as it did not break the glass, quite unfortunate. It has started to develop small spots of rust on the bare metal.

So far I have gotten quotes from 400-850, wonder if that is reasonable? I am going away for 2 months in a week's time and the garages I went to could not fit me in and I also needed to use my car. I initially wanted to fix it before I leave but it seems difficult and now that it has developed rust I am getting more afraid.

With 1 week left, is there anything I could do to prevent the rust from getting worse or would it be ok to leave it until then? Could I paint over it or apply some sort of oil to prevent further rust? I will be parking it outside and this recent storm is not really helping. I was thinking of putting a cover over the top of the car but i'm afraid the moisture might make things worse if it rains.

Thanks.

[Xcore]

Sand rust back, prep with kurust then primer and paint