Stark: Here’s a more in-depth answer than I originally planned but it snowballed.
I’ve got my hands on some OTL figures so I can make a reasonable comparison. I’m using Lascaris’s calculation that 1 hyperpyra = 0.52 pound sterling, but for the purpose of easing calculations I’m just going to say that two hyperpyra equals one pound sterling.
According to This Seat of Mars: War and the British Isles 1485-1746 by Charles Carlton, the Sovereign of the Seas, which was armed with 100 cannons, had a 1500 ton displacement, and have a very ornate and gilded stern cost 65,000 pound sterling. So the gift would pay for 3 Sovereigns. To help put that in perspective the author also gives 374,000 pound sterling as Elizabeth I’s income in 1600, so the gift by itself would be six months of her revenue at the end of her reign.
Now according to Ottoman Warfare 1500-1700 by Rhoads Murphey in one of the notes, a total of 65 million akce was needed for the Ottomans in 1653 to maintain (not build) 50 galleys and 13 galleons. I’m assuming this is for one year/campaigning season and don’t know the size of the galleons. Furthermore the author estimates the cost of building each galley at around 600,000 akce and each galleon at a minimum of 4.8 million but possibly as high as 7.5 million. For the sake of simplicity I’m going to go with 6 million per galleon.
This of course leads to the question of conversions. In Ottoman Warfare the author gives an exchange rate of 60 akce to 1 ducat in 1543. It’s a century earlier but I’m working with what I have. I’m assuming, but cannot prove, that the ducat in question is the Venetian ducat. According to a 14th-16th century currency exchange rate spreadsheet from the London School of Economics’ Website, in 1564 three Venetian ducats equaled one pound sterling, so 3 Venetian ducats = 2 hyperpyra. So the cost of a galley would be 600,000 akce = 10,000 ducats = 6,667 hyperpyra. The cost of a galleon would be 6 million akce = 100,000 ducats = 66,667 hyperpyra. So the galleon here, presumably much smaller and less ornate, costs about half of that of Sovereign.
So the gift would pay for 6 galleons or sixty galleys, or pay more than half the cost to maintain 50 galleys and 13 galleons for a year. The fleet cost comes to about 725,000 hyperpyra. Now in the context of the Indian Ocean frigates would be the best choice but I don’t know how much they cost compared to galleons/frigates, but even if a frigate still cost half that of a galleon the Romans paid for 12 Ethiopian frigates.
Now with other figures I can make at least a passing shot at a Roman military budget. According to This Seat of Mars in 1588, it cost 1700 pound sterling to maintain an infantry company for a year, 3700 for a cavalry troop, and 68000 for an artillery train (I’m assuming for the whole army). How well units match up is questionable, but I’m going to assume that an infantry company = 1 infantry droungos and one cavalry troop equals one cavalry droungoi and I’ll round the figures up to 2000 pounds sterling per infantry unit and 4 thousand per cavalry unit. So one Roman tourma with 8 infantry droungoi and 2 cavalry droungoi would cost 24000 pounds sterling or 48000 hyperpyra. Let’s add 6000 pounds/12000 hyperpyra for the artillery, so 60000 hyperpyra per tourma and 600,000 per tagma. So the eleven theme-tagmata cost 6.6 million hyperpyra annually.
Now there are four guard tagmata with 5 tourmai each, paid 50% than the provincials. So they add another 20x60000x1.5= 1.8 million hyperpyra. So we’re looking at least 8.4 million hyperpyra per year just to maintain the army, although I’d add at a bare minimum another half million at least to cover extra expenses, most likely more. This doesn’t cover the cost of fortress garrisons for example.
Now for the navy. I haven’t set down a specific navy size. I don’t know how the 65 million akce for maintenance were split between the galleys and galleons. The galleons cost much more to build but I doubt their maintenance costs are 10 times higher than galleys since they don’t have the hundreds of rowers. The Roman navy has moved much more towards galleons/fregatai so the 50 galleys to 13 galleons matchup of the 1653 Ottoman fleet doesn’t work. But I think it can safely be said that the maintenance of 50 galleys probably at least matched that of the 13 galleons so that sum going to all galleons could pay for at least 26 galleons, probably more. So 2 million hyperpyra at least for the Roman navy to pay for all its galleons, fregatai, and galleys.
So the Roman military budget is looking around 9-10 million hyperpyra for the army per year, plus 2-3 million hyperpyra for the navy. I’ve never anywhere, at least in the TL proper as far as I can tell, listed the annual income of the Roman government, save a note that the 10 million hyperpyra paid to Iskandar to gain the initial Khlat truce was “almost a full year’s revenue”. Considering the expense of the Roman military, I’m going to say that the annual Roman budget is in the 14-17 million hyperpyra range since after covering the military the entire civilian administration needs to be covered.
Everyone, please let me know if you have comments, questions, suggestions, corrections, or more data to add to the above. It'll be greatly appreciated.
JohnSmith: There will be at some point, I promise. There is a move to more linear tactics, with units firing by ranks, and smaller more manageable formations in the vein of the OTL Dutch and Swedes. The Germans are taking the lead here due to their experience in the Brothers War.