I would love to see these graphs.
The graphs got quite messy with 50+ eBay auctions over a 3-month period crammed in. I'll summarize the results instead.
Style 0: The average price was $432, the median price just $395. Normal auction prices ranged from $238 to $677; there was an anomalous $999 sale for a mint condition uke from the 1960s. Many auctions included vintage cases, but these don't seem to have affected the final price much. Nor did age. The force which drove prices was condition.
Style 0 in fair condition (playable, but with multiple hairline or worse cracks, uneven or discoloured finish, and/or missing pieces, signs of amateur repairs): average price $302 (9 auctions)
Style 0 in good condition (minimal hairline cracking or professionally repaired crack, nice finish, no missing pieces): average price $411 (12 auctions)
Style 0 in excellent condition (beautiful appearance with few or no scuffs or dings, no cracks, no missing pieces): average $573 (10 auctions). If you exclude the unusual $999 sale, a more realistic eBay average for a Style 0 in excellent condition is just $526, which is about what a new Kiwaya KTS-4 costs.
Style 1: Price range over 12 auctions was $280-$820 for one in playable condition. The average price was $511, the median price $488. In fair condition, a Style 1 brings $360; good, $487; excellent, $753.
A very rare Style 1 made 1917-1918 and in near-perfect condition went for $1200; I excluded that sale from my calculations.
Style 2: There weren't many completed auctions for these. Prices ranged from $580 to $810 (all were in fair to good condition); a very rare Ditson Style 2 sold for $1800 in a "Buy It Now" (I excluded this sale from the averages).
So there you have it. A playable vintage Martin 0, 1, or 2 is as affordable as a good solid body soprano made yesterday.
Sidenote: Prices at brick & mortar stores for vintage Martins run at least 20%-30% higher. However, they usually offer a short approval period after you receive the uke, during which you can return it. And they'll probably strum it for you over the phone if you ask nicely. Choosing to bid on eBay for similar merchandise carries a higher risk.
If you do go in search of a vintage Martin, I highly recommend first reading
The Martin Ukulele: The Little Instrument that Helped Create a Guitar Giant by Tom Walsh & John King, published September 2013. It includes a wealth of information about identifying and dating the ukes.
ETA: These prices are for USA-based auctions and shops, and do not include shipping charges.