Hmm.
So 220 ft +20 ft (dragonbone) + 20 ft (dragon 358 enhancement mentioned by Jaronk) x1.25 (large)= 325 ft range increment
325 + 90 ft from Deepwood Sniper + 25 ft from Flight arrow = 440 ft.
415 x2 x2 x1.5 (x3.5 with multiplier stacking rules) = 1540 ft.
1540*20 range increments = 30800 ft range. Or about 5.8 MILES. The game board with 1 inch 5-foot squares would need to be 513 feet long. 171 yards. For the obligatory reference, an American Football field is 120 yards long.
The bow is Strong Transmutation, CL 15th, craft magic arms and armour, far shot, true strike, creator must be an elf, price 73,800 gp. Weight 3 lb. Oh, and don't steal one. Easy way to get yourself kill-on-sight to all elves.
So we need 9 levels of deepwood sniper, 4 cragtop archer, 1 spellwarp sniper, 5 ardent.
Deepwood Sniper needs BAB: +5, Hide 4, Move Silently 4, Spot 4, Far Shot, Point Blank Shot, Weapon Focus (any bow or crossbow).
Cragtop Archer needs BAB +6, climb 10, spot 5, survival 5, far shot, mountain warrior (bab+3, survival 5 ranks)
Spellwarp sniper needs Concentration 8, spellcraft 8, point blank shot, 3rd lvl spells, sneak attack or sudden strike +1d6
Ardent is a base class.
Either way, that's min lvl 24 without cheesing for more BAB/manifesting. So let's cheese.
Shapechange/polymorph can be cast on you from a scroll. Use those to get spells (
Jaronk's summary of why this works) means you only need ardent 1. So 5 levels of fighter+ranger (2 fighter, 2 ranger, 1 warror and take sneak attack as the lvl 3 feat (UA pg 76) without losing BAB.)
Fighter 2 lvls: feats Point blank shot, far shot. Noncombatant (-2 melee attack rolls) and Vulnerable (-1 AC) as flaws let us pick up weapon focus (composite longbow) and 1 other feat. 1 lvl warrior taking sneak attack as the lvl 3 feat. 2 lvls ranger. That qualifies us for Deepwood sniper, so take that. Max spot. Get Mountain warrior in there somewhere. Pick up the Cragtop Archer, and 1 level of Ardent. Get yourself polymorphed into a creature with 3rd lvl arcane spells, or use earth power/sanctum spell (power via magic mantle)/heighten/expanded knowledge cheese to get a 3rd lvl power, class into Spellwarp sniper. Dark Chaos Feat Shuffle/other rebuild tricks if needed. Either do this as goliath (+1 LA) or take Monkey Grip (plenty of feats to spare). Lvl 20 complete, gamebreaking CON-damage artillery enabled.