eGPU I would recomend Gigabyte AORUS GTX 1070 Gaming Box Portable Graphics Card. It cost under 600 including a GTX 1070 (now £ 569.98 at ebuyer). For laptops Lenovo offer decen quality-price. Lenovo has offers now for the Lenovo Yoga 720 that has thunderbolt 3, there is a model with a i7 for £850 for example. Still lower price than Surface and you get much better spects (including a full size GTX1070 vs a mobile capped 1050).
Looks like they are out of stock on all 15inch variants
Which eGPU dock and specific machine would you recommend?
Do Amazon not have the 15inch model?