Is it possible to enchant armor high enough so that the cost of destruction spells are reduced 100%, so that no magicka is expended. Also, if this is possible, would I still need to have 430 magicka to cast the master flame spell, or would I be able to cast it with 10 magicka?

yes and no you dont need any magicka to cast any spells then

you need to get to 100 enchanting and perk up the right branch of enchanting and you will get to 25% per item, that's ring, neck, chest and pff cant remember what the last one can ench magic use.
if you get the last perk in enchanting you can do that to 2 schools of magic.

Personally i find it a bit overpowering, so what i do is wear the archmage robe and the rest enchanted to 25+% with pots. You get 90%+ reduction on two schools and the others -15% wich is quite ok. by that time you will have at least about 300 of a mana pool and that is quite sufficient to cast mostly everything of interest. Have fun with your mage

Yes, you can enchant 4 pieces of gear with -25% casting cost when you have Enchanting at 100 and all relevant perks (5/5 Enchanter, Insightful Enchanter) to get -100% cost. At that point, you need zero magicka to cast any spell from the relevant school. Use Grand souls to make the casting gear.

-Loth

Darn. now I realize that I've wasted 20 levels worth of points on magicka. >.<

Welcome to the wonderful world of horribly unbalanced systems and turning your game into a quasi-godmode snorefest.

Ha, don't be down, man! Just because you can enchant stuff to cast 2 schools for free doesn't mean that the other 3 schools don't need magicka.
-Loth

Do you really honestly think that free cast destruction is that much more powerful than fully perked duel wielding?

This is exactly what I do on my mage, I use the archmage robes and various other enchanted clothes I have made. It adds up to ~92%, I have a magicka pool of 600 ish, so I can cast a good few destro spells.

Having 100% reduction is ridiculous, ruins the game for me. I end up with ~92% destro, ~40% conjuration, ~40% illusion and ~70% alteration something like that. Works well for me.

Wait, I thought that each school had an armor enchantment that could reduce the magicka cost. I'm sure that I have three types of robes at the moment that reduce the cost.

No, you're right... there are enchantments to fortify every single spell school. It is up to you to determine how you want to use them (if at all). Many folks are like me, and don't stack enchants to fortify just one school... we spread them out over the ones we use the most to lower casting costs in general for ourselves. You might discover that having a -50% to four schools is more fun to play than having a -100% to two schools, for example.

-Loth

PS you can enchant more than just robes with the fortify [magic school] effect. Rings, necklaces, and circlets/helmets also take the enchantment.