Stat-boosting items rather conveniently cost the same as resistance items and armor bonuses.

+1 stat, resist, or armor = 1,000 gp
+2 = 4,000 gp
+3 = 9,000 gp
+4 = 16,000 gp
+5 = 25,000 gp
+6 (stat, or bracers of armor) = 36,000 gp
+7 (bracers of armor) = 49,000 gp
+8 = 64,000 gp

Do note that some things are considered epic, and would probably be hard to come by:
1. armor with a +6 or higher enhancement bonus, or a total bonus of +11 or higher
2. stat-boosting items that give +7 or more
3. a resistance item that gives +6 or more
4. bracers of armor that give +9 or more

Given how some schools don't really benefit from Extend Spell, narrowing the rod to a single school doesn't lessen its value much. For instance, Abjuration and Transmutation both benefit a great deal from Extend. Divination and Evocation? Not so much.

I'd say shave 10% off the price, personally, but you could go as far as 20%, depending on how much power you want to put into the hands of the PCs. If the party's wizard loves to load up on polymorph, fly, and other transmutations, he won't care whether it's a normal rod or one that only works with transmutations.

Jared Rinseth - Human Assaultmage/Anarch of Shyr, uses a pair of shortswords but frequently throws them and draws another one of his 10. - I'm thinking some kind of Omnislash v.5-esque teleport based attack that's based on his plot swords (so far he only has two, but I plan on giving him the opportunity to get the other 8). Each sword will have a different attribute (flaming, cold, poison, lightning, vorpal, etc.).

Andras - Water Genasi Shieldmage/Water Elemental, since he's an elemental due to plot stuff I let him use his Swiftcurrent as a regular move action rather than an encounter, he typically moves to flank and whenever there's a spare moment he shields. - To be honest I'm not entirely sure here. So far all I've got is something to give him better flanking bonuses, move further, and shield more damage but it seems kinda... lame in comparison to the other two.

Daivos - Deva Snaremage/Sage of Fate's Bond, he uses terrain more strategically than the other two and often collapses caves/bridges/trees on enemies by making them attack the support structures - Since some of the plot has to do with his previous lives and their failure to prevent what's happening, I've been considering letting him use MoTL freely and letting him manifest one of his previous lives when he uses glamor blade and having it be a fully separate creature.

I can speak to the Shieldmage, since I'm playing an epic one now. In this party, he's your healbot, or as close as you've got, so you could crank that side of things - increase the damage prevented, the range, or give that feat that allows the first use of the aegis to not count as the PC's immediate action (essentially, this lets you use it twice per round). Or... there's a neat swordmage power that allows the shieldmage to bounce the damage they prevent onto the attacker - it's a daily, so make it an encounter power or some other more-useful rate. It boosts effectiveness nicely and captures a great flavor.