Any ideas what cheap motherboard are best for 1050ti?
this really depends on the CPU you want to go with, as this decides the chipset your motherboard will need to have.
As I assume you're on a very tight budget the best option buying new is probably a ryzen 3 3100, although this comes in at a still rather pricey ~110€.
If you went with that you could get an Asus Prime A320M-K for just 60€ and spend a farther 60€ on 16 GB of DDR4 RAM, coming to around 240€. Plus there's a good chance you'd need a new PSU which would be another 40€.
Is that in your price range or do you need to go cheaper?
Looking at your system a full upgrade is needed as ChumP said so I don't think you'll end up under 300€ (before the GPU) for a full upgrade.