I seriously doubt that the sizes will have a price difference. These are meant to be fitment choices and encourage people to buy the bigger watch if they are comfortable wearing it. The gold watch will even be priced appropriately to cover both sizes at one price point.
So, my predictions, based on more time spent in the watch industry than with computers. My father was a watch repairman, I sat on his lap and watched him fix watches when I was a kid, and I've always been a fan and had a collection of timepieces.
Sport: $349 with a colorful sport band. Either aluminum color.
Watch: $499, but justified with the inclusion of a $80-$100 band option. So, essentially, it's not a significant change in price as the Sport + an upgraded band would be able the same. This watch just isn't available with the sport band out of the box so the price of admission is higher. Either steel color.
Edition: $7,999 in your choice of yellow or rose. Possibly not sold without an appointment, and frankly - hard to picture anyone picking it up at an Apple store. Maybe a partner jeweler will be announced.
Bands, cheapest to most expensive
Sport Band $50ish
Leather Loop $80ish
Classic Buckle $100ish
Modern Buckle (non-gold) $150ish
Link Bracelet $200ish
Milanese Loop (this is going to be pricier than you expect) $250ish, maybe $300ish.
Modern Buckle (yellow or rose gold) included with edition, not available seperately, replacements only available to owners of the watch at an undisclosed price.
I'm suspecting I'd be spending around $800 on launch day for a steel watch with something leather and a link or milanese bracelet especially because I'm fond of 'beads of rice' bracelets, which is echoed a bit in the Milanese loop design. I like to have a summer and winter strap or bracelet options for watches where changing it is practical.
That being said, I'm surprised no one has yet echoed the purpose of a multi-thousand dollar gold watch - so you can buy a watch for a few hundred and say 'this is the same watch people are paying x thousand for' - that watch existing in the product line makes your inexpensive model have more perceived value.
Having a 'cheap' version of a exclusive watch in most luxury brands would be a disaster - a platinum whatever on a bracelet for $50,000 would take a hit in status and sales if a steel 'version' that looked 90% the same at a discount. In this case, the purpose of building the gold watch is to actually legitimize the cost of the lower model and Apple doesn't care how many they will sell.
There's my guess - I'm excited to see how it all pans out.