We have our mail redirected to our sons house for up to 4 mths at a time and it costs us less than $20 for the full time. Just ask at the PO, fill out the form and you have to give several days notice. Not expensive.
Costs are: $19 for 1 month, $32.60 for 3 months, $48.85 for 6 months and $84.70 for a year - buggered if I can figure out how they came up with those prices
As all of our kids rent and move around a bit we're going to redirect to a PO Box and get one of the kids to collect the mail, scan it and send it to us via email - that's the plan at least.