Looks like a high-end Surface Book with an i7 CPU, 16GB RAM, 1TB disk, and an 18-month subscription (minimum) is gonna run $220./month before taxes & fees.
That's something over $4000 with the taxes.
Whereas at the low-end, a Surface 3 with an Atom CPU, 2GB RAM, 64GB disk, and 18-month subscription will run about $50./month.
About $900. total.