>>55290752First off, Porygon costs 6500 in Blue, a much bigger discrepancy.
Second off, Dratini costs less in Red than it does in Blue because in Blue Dratini is taking Scyther's spot as the second most expensive Pokemon, while Scyther's Blue counterpart, Pinsir, takes Dratini's spot as the least expensive Pokemon.
And in both cases those slots are less expensive than the Red version.
To put it another way, it takes 20179 coins to get every Pokemon in the Game Corner in Pokemon Red, while in Blue it only takes 15670 coins.
Unsurprisingly Clefairy costing 250 more coins in Blue does not make up for Porygon jumping up 3500 coins in price.