Reddit mentions of Garmin 010-11023-00 Colorado/Oregon Series Bike Mount

This looks like the right one for your GPS. Can't say much about it as my GPS is much older so uses a different style mount. But you can't beat the price of this one.

http://www.amazon.com/Garmin-010-11023-00-Colorado-Oregon-Series/dp/B0012MI7QE

*Edit:
There's some conflicting answers on the Amazon page about whether or not this is for the eTrex 10. Garmin website recommends this product number as well:

https://buy.garmin.com/en-US/US/shop-by-accessories/mounts/bike-cart-mount/prod11411_010-11023-00.html

I have a Garmin Oregon 450 that is ~5 years old. Despite it being a bit of a pain to use load maps onto, it has worked really well for touring. Some generic Costco brand AA batteries last ~15 hours of constant use. Pretty much get 2 days of riding of a pair. If you bought brand name you could probably do better. A quick ebay search shows factory refurbs going fro ~180, I don't know if that is a good price but these things are tough so a factory inspected device will last.

Pros:

• Durable and long lasting. I have had mine for, I said, ~5 years and it still works great
  
• Waterproof for when you are biking in the rain
  
• Accurate metrics including elevation gain and loss data
  
• clear route tracks to follow
  
• Back lit so you can see it in the dark
  
• Garmin Connect allows you to upload your rides and data to the cloud
  
  Cons:
  
• Loading Google map data although once you figure it out it's not that bad
  
  To load Google maps onto the device, you need to go to Google Maps creator and export your map as a KML. Then there are a few sites that will convert your KML file to GPX which is the standard Garmin file type. This isn't so bad if you plan ahead but certainly not as easy punching an address into Google maps on a smart phone. Then again, a smartphone's batteries won't last that long or have reception in the middle of no where. If you want help with this feel free to PM me.
  
  I have a this bike mount. It works well.