What dgillz says is absolutely correct. The most flexibile solution is the EDI solution. In the end you pay about the same, but you end up with a product that can change with your business, so that as requirements change so can your solution.
If you wish to delve in to the world of writing this custom, it may be much less daunting than dgillz states. The 25 table figure comes from adding up tables touched for inventory allocations, serialization, features and options, complicated price structures, auditing, history, etc... The less complex your situation, the less complex your solution will have to be. In a situation where you will be importing orders for non-stocked/non-controlled items, you will only have to build the OEORDHDR_SQL, OEORDLIN_SQL, and the OELINCMT_SQL tables.
Scott Travis
infoSpring, LLC.