PocketCloud Explore lets you dig around your PC's files for free—at least if you need to do so only on a single PC, and don't need to transfer anything bigger than 25MB.
PocketCloud Explore presents you with your PC's folder tree once you've installed companion software on your computer and booted up the app. Now you can navigate your hard drive until you find the file you're looking for. Selecting a file opens it in a native Android app.
It's especially great for accessing documents and Office-type files. A $5 per month premium subscription ditches the ads, unlocks remote access for up to 10 PCs, and ups the file size limit to 1GB.