$20 for 10 prefilled cartos is actually a good price if they have decent juice and soft-caps on the mouth end for easy refilling (if they have hard or glued on caps, then it's not such a great deal). Smoketip is fortunately KR808D-1 so it should be able to use any KR808D-1 prefilled or blank cartos including the Vapor4Life ones. The Vapor4Life ones are a bit more expensive but I know those have soft end caps you can easily pop out with the end of an unbent paper clip to add juice.
Always add juice before the carto runs dry. If you run them dry you can singe the stuffing and then it will be stuck with the burnt taste. Whenever my carto's vapor gets a bit light or a bit dry, I first try tilting the ecig carto down for a few seconds. If that doesn't revive the vapor, then it needs more juice. I take the carto off the battery when I add juice (especially important since Smoketip is probably an auto battery and can be killed by juice drips onto the threaded end of the battery because of the drag sensor there). And I usually hold a bit of tissue on the threaded end of the carto in case a drip comes through and to clean up after filling, if needed. I puff into the threaded end to try to make sure the air channel is clear. Then I use it.
This is a video about filling a blank. I use a plain small paper clip since the caps of V4L cartos are all soft now. And i do rotate the carto when filling because the stuffing seems to be a little tighter these days and absorbs a bit slower. And interesting section of this video is how he straightens the air channel. You don't have to do this all the time. But if a carto gets hard to drag or you can't see light through it, then the air channel is crooked and can cause much tighter drags or even block the flow of vapor. When that happens I straighten the channel to get more use out of the carto.
YouTube - How-to guide to refilling KR808D-1 or Vapor King cartomizers
Another thing I use is a plastic or delrin V4L or KR808D-1 drip tip (from LiteCigUSA.net) on the end of a carto instead of the little white mouth end cap. No tools needed to remove the drip tip and add a bit of juice. And it keeps my lips cool when I have a hot carto. Don't drip through it though - it would probably aim the juice at the air channel.