Can anyone give me the ballpark figure it costs to build a 4 plex? Don't plan on doing anything fancy inside and they will probably be 2/2 900 sqft each. This is in south Louisiana btw.
While I don't have a specific answer for you maybe I can help point you in the right direction.
Most builders can/will quote you their cost/sq ft to build a house/property. I know in my area (DeRidder, LA), which is around 2 hrs from your market, builders cost around $110/sqft for single family homes new construction. This may be different for a 4 plex being there are more kitchens, bathrooms, plumbing, electrical and HVAC.
Either way, a reputable builder should be able to give you an estimate, they may even have spec build plans available for a 4 plex. If so they would probably do a spec build at a lower rate being they could use all of their normal materials and are familiar with the layout/design so they could do them more efficiently.
Every market is different, so I can't give you an exact amount. Hopefully I've pointed you in the right direction though.