Automated Vehicle, the level 30 spell from Mechanical Mastery, would allow for a flying vehicle on the basis of more non-magical flight. The spell states that it can substitute for a dozen horses. Assuming this means not peak performance, but long-term performance, that's equivalent to a... well, 12-horse-power engine (though peak performance of a horse is just under 15 hp, we want our aircraft to fly for a long time).
Now, a Fokker E.1 Eindecker from WW1 had a mass of about 560 kilogramms (just over a 1,100 pounds) and had an 80 hp engine, so about six Enchantments. That would be winged flight at about 120 km/h. An example for an early helicopter might be the Sikorsky R-4, with a 185 hp engine (so that would be about 15 enchantments), which had a starting mass of 1,200 kilograms, or 2,500 pounds. So, for much effort, we'd still not get flying ships, but at least small single-seater aircraft. A single enchantment of Automated Vehicle will cost 16,704 silver pieces, though.
A Large construct would be equivalent to these craft in weight. Properly shaped, could it be strong enough to carry a rider or two? It seems so, as per section 5.4 of RMU Treasure Law, which explicitly offers the option of flight for constructs and golems. If I understand the rules correctly, creating a Construct is a simple level 13 enchantment, which would cost 3828 silver pieces to enchant, PLUS the material cost (for good steel, that would be something like 2,500 silver pieces for a 1.25-ton-construct) and the cost of crafting the construct inside and out (the latter should be in the range of 2 sp per working day, I would guess). Certainly a much cheaper option than building an airplane or helicopter as described above, but still not cheap.
RMU Treasure Law hints at another option, though: One that is even cheaper.
On page 23, Table 2-2a: Animals lists, among other things:
"Dracasus 1200 Trained as a mount; takes to combat naturally"
In the beta file of Creature law, the following description is found:
"Dracasus:
Appearing very much like a serpentine Pegasus, a Dracasus has bat wings rather than feathered ones,
scales rather than hair, and a fin rather than a mane. The beast’s tail is very Dragon-like, and the feet are
clawed rather than hoofed. It boasts a 40' wingspan. The Dracasus is a strange creature. It is thought by
some to be a fell beast, and by some to be a demonic Pegasus. The latter seems hardly to be true, as a
Dracasus can be trained to be a fine and noble steed. Like Pegasi, they can make wonderful mounts if
trained properly. As a trained mount it can carry 600 Lbs without penalty, and gives the rider a special
bonus of +10 to all Riding maneuvers. There is said to be a wild herd of fire breathing Dracasus that
dwell on some distant mountain range. The Dracasus is an omnivore, and eats birds, rodents and small
cattle and deer as well as grass, oats and more traditional equine food. It can weather cold climes much
better than most reptiles, often nesting on high rocky spires amid arctic winds. In combat, the Dracasus
swoops down upon its opponents and rams the victim down or slashes with its claws. On the ground, it
tramples foes like a horse after charging. Its bite can also be quite vicious."
So assuming that this animal is typical for flying creatures of rideable size (FCRS?), at least in terms of price, it's certainly a more affordable option than any of the others, while still not being an everyday occurence.
