Well, $15 (today's conversion rate) for me and very well worth it as it helps support the forum.
That makes it:
1.25 a month
0.29 a week
0.04 a day
Probably the second best train forum bargain on the 'net!
The first is the OGR* forum at $10 a year.
I do both and the enjoyment from them just can not be measured monetarily.
*O Gauge Railroading magazine sponsors it. There are at least two of us here on both.