Another option is to use a Line 6 Variax.
It has an alternate tuning function that can be applied to all of the internally modeled guitars.
So if you are cunning and are quick with your hands, you can switch the model on and off, moving between standard tuning (or any other that is your main stay tuning) to drop D or C# or whatever.
I expect you could pick up a second hand JTV fairly reasonably. I have a 59 and use it for all kinds of different tunings from open D to odd C# tunings and straight Eb and drop D etc.
The Workbench programme lets you assign your own tunings so you can even have a go at emulating mandolins. You can store these on the guitar and arrange in order if you so wish.
Some models work better than others but with a bit of tweaking and testing you can get in the ball park for almost anything. There can be a little warble on lower notes but this is offset by the convenience of not bringing four guitars and constantly changing during a set.
I find there is less latency than the Kemper’s de-tuning feature (which is very good by the way and I have used at other times) and I add coded notes to my remote screen to remind me which model and tuning to select before each song.
This is not a cheap or immediate fix for you but as a working tool, it does a good job. I have even used the acoustic models with alternative tuning for a duo act. This is acceptable if I play carefully and keep the EQ closely matched to the model so that it smooths out a little.
Good luck, I hope you find a solution.
Cheers
Pre-Amp