hi, your probably need an engineer to advise you the type and the piling contractor to advise the cost.
before knowing what's needed, they will need to know what kind of structure and how many storeys you are building to determine the load and .
I guess cheapest pile will be Reinforced Concrete (RC) pile if your site permit.
I just did 8 micro piles (average 16m depth) for an extension, just for 4 new columns to carry a 2 storey structure. The piling cost close to $19K. excluding engineer fee, RTO, and soil investigation.