My proposal is feasible, both in price and time needed to implement it. We could start churning these out tomorrow and have dozens of them in place by the end of next month. What ya'll want is going to be a much, much more expensive and time consuming endeavor.
Here's one method of spreading Protection from Evil to as many Legion soldiers as possible. It's the only remotely practical method I can think of.
First we start with Protection from Evil. It's a 1st level spell, but we'll be casting it at 11th level due to the necessary Metamagics.
Then we add
Reach Spell to it, and not the shitty D&D version, which wouldn't be feasible at all, but the Pathfinder version which is quite nice (though DP would have to make an exception to allow us to use it). This will be a +2 spell level increase, in order to give the banner pole a range of 210 feet. If we only increased it by +1, the banner pole's range would be just 50 feet, and that would make it very difficult to keep very many Legion soldiers protected.
Next comes Chain Spell, in order to allow each casting of the spell to affect more people. The minimum caster level of the banner pole is 11th, so each casting will affect up to 12 people. This increases the spell level by another +3.
Now our spell is up to 6th level with a caster level of 11th. If it activates as often as possible, ten times per minute, it would be able to affect 120 people per minute, each of whom would be warded by Protection from Evil for 11 minutes. Assuming maximum possible efficiency, the banner pole could ward up to 1,320 Legion soldiers without allowing the effect to fall off any of them, so long as they stayed within range.
(6 x 11) x 1,800 = 118,800 gold / 10 = 11,880 IM (59 enchanting days)
If we increase the Reach Spell level adjustment to +3 in order to give it a range of 920 feet, the banner pole would instead have a minimum caster level of 13th the the Protection from Evil effect would be the equivalent to a 7th level spell. In that case, each casting of the spell would affect 14 people, or 140 per minute, and up to 1,820 could be warded continuously, again assuming maximum efficiency.
(7 x 13) x 1,800 = 163,800 gold / 10 = 16,380 IM (81.9 enchanting days)
And if we add Extend Spell into the mix, the Protection from Evil becomes an 8th level spell with a minimum caster level of 15th. Range would increase to 1,000 feet and 160 people per minute could be affected, up to 2,400.
(8 x 15) x 1,800 = 216,000 gold / 10 = 21,600 IM (108 enchanting days)
My apologies for getting overly pedantic here, but I'm just trying to be realistic about what we can reasonably accomplish. If ya'll want to do this, my advice would be to immediately go to Armun Kelisk
and the Opaline Vault and commission ten of them in each. The last of the three I provided pricing for would be the most expensive and take the longest, but would also be the most practical, given the potential range of the effect and how many people could be affected. In a little over 3.5 months we could have enough enchanted banner poles to protect 48,000 Legion soldiers, at a combined price of 864,000 IM (remember, market price is double what we pay to enchant stuff on our own).