First issue is, you're not going to transfer "live" HD video via USB 2.0 connection. You can transfer files after the recording, but not usually during.
Second, there are capture cards such as BlackMagic Intensity or Matrox MXO2 Mini that will accept an HDMI input and capture high-quality live video to the PC. However, many DSLR cameras, even though they have an HDMI output, will put out a non-standard signal. Meaning it is cropped, or perhaps has some viewfinder info overlays in the picture which can not be turned off in the menu, making the HDMI output unsuitable for recording. This has been a huge problem for DSLR film makers that want to use external recording devices like the Atomos Ninja 2. Some of the newer DSLRs can now output a proper, recordable signal, after much complaing from customers.
Bottom line, money is always a factor, but a DSLR is the last camera I would ever try to use for long-form events. There has to be something you can borrow or buy cheap second-hand, meaning a camcorder. But even then, you need some kind of capture card to get the live video into the computer, unless using a DV or HDV camera and then you can use 1394 (Firewire) into computer. DSLRs are just not practical for a lot of video tasks, sorry.
Jeff Pulera