I just went through this on my Duster, it AIN'T cheap!
I don't have the exact figure but if you do a top notch job and get EVERYTHING new or restored you can easily spend 5-6K on an interior. Even more if you are talking about farming out the steering column, foot pedals, heater box, e-brake assembly rebuilds, etc.
Personal real life example:
I stripped my own seats to the springs, made neccesary repairs, painted them, and delivered them along with my new Legendary seat covers ($1,080.00) to the upholstery shop. I elected to go with all new foam as well (nothing like a brand new interior that smells like a rotten mouse nest) so new foam and top shelf install job came out to another $705.00. Mind you that this is for a base model bench seat front and rear (plaid cloth inserts made covers more expensive than plain vinyl).
I bought a headliner from SMS ($200.00), door panels, arm rest bases, roof insulation kit, firewall insulation, under dash insulation, insulation clips, package tray, trunk divider, sun visors, tips, door panel clips, sail panel boards, bench seat hinge covers, glove box liner, from Dante's ($899.00) a ship flat carpet set from ECS (around $375.00?) seat belt restoration by Snake Oil ($800.00) dash cluster restoration by GCAR ($1,200.00) dash pad from BE&A ($200.00) NOS arm rest pads $150.00, etc. This does not include restoring the foot pedals, heater box, e-brake assembly, or the steering column or steering wheel, and I havn't factored in some misc. small parts and labor to install the headliner.
Adds up quick!