When I sent my horses out on lease, I sent all tack (bridle, bit, martingale, saddle, saddle pad, boots, girth) and blankets.
My horses are also a bit difficult to fit (because they are so wide) I struggled a bit with the idea of sending my saddle, but not because of the expense (it was a County), but because at the time, I still needed a saddle for my other horse (the two horses shared a saddle). I ended up buying a much less expensive saddle that fit my horses (a Thornhill) and sent that one on lease. Yes, it was an additional expense for me, but it definitely gave me peace of mind I wouldn’t have had otherwise (and in the grand scheme, since I wouldn’t be paying for the horse’s monthly expenses, I still came out ahead).
Regarding the expense of the saddle though, when I posted this similar question on here, it was pointed out to me that I was sending my horse out on lease, which was probably a more valuable item, so if I didn’t trust someone enough with my saddle, why would I trust them with my horse?
Every item I sent on lease with my horses was documented in an itemized inventory with a very specific description and value. It was clearly outlined in the lease that should any of these items become damaged or go missing, the leasee was responsible for replacing them with either a new version of the same item or an item of comparable quality (which had to be okayed by me). This didn’t work perfectly, of course (and I didn’t expect it to), but I had made it a point to not send my best-quality stuff.