I am doing the GHG conversion course in about 2 weeks! I already use gelish and love it!
I am doing the evolution course which is roughly £180 but then you need the kit too.
I am only doing that as it involves sculpting which I have not done before and I thought the 2 day would be better for me.
If you are confident in Hard gel then you can do a one day course which is about £90 something.
I would go on Nail Harmony site and email your nearest tutor. Mine is really lovely and got back to me really quickly with all the info.