Monthly plan or a one-off purchase
The choice is decided by how many runs you do a month. The price per address misleads here.
Where the line falls
A monthly plan wins once collection happens more often than weekly. A one-off purchase suits rare, large runs.
Count runs. A cheap address idle for three weeks costs more than a rented one working every day.
What a one-off purchase costs you
Setup time on every occasion: load the list, verify it, distribute it across threads. On regular work that is hours a month.
And predictability: a new set each time, with behaviour under load unknown until the first run.
What a monthly plan costs you
You pay through the weeks with no collection. If your work is seasonal, that is real money.
The fix is a smaller standing set plus a top-up in peak months.
The calculation
Take runs per quarter, multiply by the cost of a one-off set, compare against three months of the plan. The answer is usually obvious.
runs per month 8 one-off 8 x cost of a set monthly plan 1 x monthly fee break-even around 4 runs