Familiar with Tamiya Tiger 1?

Agree with Roy....100%...rubber band tracks CAN be used successfully, if the builder has the appropriate skill level. I have done it myself. Your post gives me the impression that you are entering into a commercial agreement without the confidence/experience/ to execute it. Nothing personal, but an experienced builder would not have to ask these questions, IMHO

My experience is this...once you deliver a build and have been paid, you're work is out there for other prospective customers to look at. If it is skillfully done OOB, that lends more to your credibility than "buying" realism using AM parts.

In other words, your work is not just to satisfy one customer, but is an investment to get future business. It makes a statement. If you don't pull it off...well, you probably won't get another commission.

Since it's a commission build, your best route is to gauge your customer's interest in add-ons relative to the cost.

PE?  Barrel?  I highly doubt your buyer would want the added expense of these add-ons (plus your additional labor).  I wouldn't even bring in aftrmkt tracks whatsoever. 

If I were you, I'd avoid the discussion about add-ons completely.  It's a business deal.  You don't want this:

"the basic tank is $100 but it'll be $200 if I want PE and a metal barrel?  What are those? $300$ if I want 'froo-ill' tracks?  Are you crazy?"

All the while he  fears you're ripping him off.   Don't do it. Nor should you undersell the value of the service you provide. Commission build buyers want a nice desk/bookcase ornament, that's all.

Since you have little knowledge of PE/Barrels/tracks for this model, I suspect you're not a long-time model builder.  Even all the more reason to deliver a simple product, at a fair price, in order to assure a happy customer.

To be frank, if someone were to inquire of me to provide a top level, well detailed and painted Tiger 1 commission build, I'd charge $200-300 and provide him with a DML Tiger 1 kit.  Well detailed and not needing more add-ons. 

I have the Initial and early production kits, and seeing as they came afer the Mid and from what Stik has said about the late kit, I would guess the two I have also have Indy Link tracks.

I have the Tamiya mid and late production kits in my stash. Both of those have indy link tracks. I don't know about their initial or early production kits. I built their original 1970s vintage Tiger I kit about 30 years ago and still have it. That one has "rubber band" tracks that are pretty much standard for that era from them. Detailed outer surface with no detail beyond the guide teeth for the inner surface. Does that sound like what you have?

Which kit is it, Tamiya have several Tiger I kits. The Mid production kit, 35194, has indy link tracks. I have 2 of their other Tiger I's in the stash but can't remember which tracks they have off the top of my head.

There is lots of AM out there, I have Fruil tracks for all mine and lots of PE, but it just depends how far you want to go.