I'm using something called 'My Private Network', which I pay about 8AUD a month. Might not be the best but it works for me. There are plenty of good ones if you Google. I'm only using VPN when I'm back for mostly 2-3 months so the VPN won't cost much.
You will need a router that allows you to set up VPN on it directly, ideally a router that is flashed with DD-WRT should work well. However, if you are just planning to use it for streaming, a DNS service should be the best bet for you since you will still be able to get your local IP address and access US contents for Roku.
Creating a US Roku account might need a VPN though, the standard VPN package comes bundled with DNS so you can use either one for your needs.
My Private Network