Get someone to run an OM3 (or better) fiber.
Friends don't let friends run multimode. Pull 6 pairs 9/125 single mode plenum grade cable and splice them to a small wall box in both ends. Bonus: There is an opportunity to buy gear and learn something, if you don't already own a splicer and know how to use it. (If you did, though, this would be a no-brainer. So am guessing not)
On those distances it'll do 100G with (relatively) cheap transceivers. 10GE is like 15 USD from the likes of fs,com up to 10km.
Edit: The installation of cable is probably equally expensive whether fiber or copper, per meter. If you can reach a place where there's telco grade (i.e. Cat 3 or lower) wiring to your present office, short-range DSL looks OK,
BUT there always is the problem of mixing different *DSL encoding schemes in the same multipair cable. The systems that are assymetric, like ADSL and VDSL, count on the pseudo-interference situation of all pairs going the same direction and therefore noise being somewhat predictable. A link going the other way, like having the "CO" end in the office and the "subscriber" end in the basement, might wreak havoc with other peoples connections.
I
THINK but my memories are shady, that SDSL (2 Mbit symmetric) is kinder in this regard, and will work.
Still, if you have the least chance of getting approval, I'd say fiber (and there I mean single mode and ONLY single mode) is very high on the desirability scale.