Transaction fees (including the spread cost) on cryptocurrency exchanges are typically a percentage rather than a fixed amount. So it doesn't matter if you do $100 every week or $400 every four weeks.
My point about doing 30 trades every week manually is a lot still stands though. Maybe I'll try scripting this with Bittrex's API. It would be cool to have an option to scale each trade size by the current relative market cap, so you can have your own crypto index fund.