What are you looking to do? What's your environment?
Starting a rural WISP with a single DSL feed and private IPs (NAT'd) when you have free access to silos/grain elevators in exchange for internet access isn't that expensive.
Starting a multihomed business class ISP in a dense urban environment with public IPs & lots of bandwidth to clients is quite expensive.
To use a MT based solution, I can give you a rough cost idea for some of our hardware we're using in the field:
My costs may be a bit off, I don't do the purchasing, but it's close.
APs: RB532, enclosure, SR5, sector antenna, cables/grounding/etc:
RB532: $140 or so.
Sector antenna: $150
Rough AP cost: ~$500
For a CPE, we use a RB112, CM9, and Rootenna:
Rough CPE cost: ~$250
You can get much cheaper CPEs (Tranzeo, etc), but they can be a bit of a pain to deal with.
Bandwidth isn't cheap either. For 10Mbit of fiber, with a few blocks of IPs, you'll be looking at over $1000/mo.