This was a big topic and mod on the CTX forum. The Tutoro seemed to be the go-to that most of the CTX riders used.
Rebel, on this forum, put his own together for less than $20! I copied his design and it works well, although I don't have it on my Versys but did have it on my CTX.
Basically, you can get some fuel line-type tubing from an auto store or Home Depot, zip ties, a bulb (I bought a 4-pack for $3 on eBay) and a small plastic bottle from Walmart in the travel-size section (You'll have to add another hole in the top for a breather tube). I found a small airbrush bottle at Hobby Lobby in the paint/model section for $5 and it already has two holes. You'll have to fabricate something to hold the bulb. I used a little square piece of metal, drilled a few holes and mounted it behind my rear peg. A simple press will get the oil on the chain.
Hopefully you get the idea but you can YouTube DIY oilers and get a better understanding.
***Personally, I almost prefer to clean and lube. Sure, it's a PITA but it allows/forces me to check out the tires for any nails, leaks, etc since it's up on the center stand and my eyes are down there anyway!