Xisef,
You mentioned that you would need new hardware to go from 3 to 5 boxing. What are your current system spec's? Depending on your geographic location I'd imagine someone here could come up with a Newegg list for $700 USD or less, excluding a monitor.

With the free month that you get when you upgrade a trial account you may want to consider keeping 5 accounts going in order to maximize your level gifts while minimizing your transfer costs.

Account 1 (Ximycall)
Account 2 (Xiearth) Refers Account 4
Account 3 (Xistorm) Refers Account 5
Account 4 (Xiheed)
Account 5 (Ximycall)

Cost Month 1 = $14.95 x 3 (Account 1, 2, 3) (Accounts 4, 5 are under the 30 day freebie)
Cost Month 2 = $14.95 x 3 (Account 1, 4, 5) (Accounts 2, 3 free month from paid month account 2, 3)
Cost Month 3 = $14.95 x 5
Total: $164.45
Compared to
Cost Month 1 = $14.95 (Account 1) (Account 2, 3 are under 30 day freebie) + $50.00 (transfers)
Cost Month 2 = $14.95 x 2 (Account 2, 3) (Account 1, free month from paid month account 2)
Cost Month 3 = $14.95 x 2 (Account 2, 3) (Account 1, free month from paid month account 3)
TBD $50.00 (tranfers)
Total: $174.75

The only problem is Ximycall loses out on the 3x xp but you will get 4 60's in the time in a fraction of the time. For example, my druids did 1-60 questing, in under 2 days (with about 400 gold invested for critical spells / mounts). If you have a higher level to boost the duo through you can really shorten the time, down to 18 hours or less.

Edit: Clarity! Math!

-Stav