I buy from ebay.com
You can get a 6 months supply of Kirkland minoxidil solution for around $40 with international shipping.
Regarding brands, Rogaine/Regaine/Kirkland seem to be the most popular ones, hen you have less popular ones like Qgain and Folligan. I'd stick to the former ones mentioned.
Kirkland is most value for money where Rogaine/Regaine are always going to be expensive.
I wouldn't rush and buy a 6-12 months supply of liquid minoxidil solution as you may find yourself allergic to the PG, meaning you'll have unbearable itching and irritation which would not be pleasant. Perhaps start with a 3 months supply and if everything is okay then you can keep a 6 or 12 months supply for your next order.
If you find yourself suffer from the itching/irritation I mentioned, you should try minoxidil foam, also offered by Kirkland and Rogaine/Regaine, which does not contain PG. However, if you're allergic to the PG, do not buy Qgain minoxidil foam, because even tho it is quite cheap, it does contain PG.