As jncraton noted LEGO is going through a transitional time now. Sadly trains are not a huge portion of their sales so it tends to ebb and flow through time anyway. So if you want a train definitely grab it while it is for sale widely. If you wait a year or two it could be gone or harder to find.
There are other options however...
Buy new trains on the aftermarket
You can spend crazy money on old LEGO trains. But there are recent trains that are available at reasonable prices:
Be careful to not go too far back. If you go far enough back track is different and you will run into compatibility issues. The first book I mention in the next section does a good job of going through the history, but it doesn't get into the 2018 trains or their electronics.
Build with instructions
There are a few books on building trains in LEGO:
I've got the one above. It goes into part by part detail on several train and train car designs. The designs are flexible in that you can change the colors. There are folks who make labels that compatible with these designs as well. I haven't managed to build any of these yet, but I'm working on gathering the parts.
There's another book that came out this year: https://brickset.com/sets/ISBN1513261134-1/Build-It!-Trains
I don't have this one yet, but it looks like it has potential. When it arrives I'll edit this somehow.