then there's also the "90 day" rule - no passengers unless you have made 3 take offs and 3 landings in the last 90 days
As a side note, these 3 T/O and L/D (hopefully the same number

) can be done very easily if you decide to go for a flight. Just go up and do 3 circuits and you're 'legal' again....thats not to say safe of course. The club I'm with have a 28 day rule, if you haven't flown for 28 days then they want you to do 3 circuits with the instructor. This is fine as the instructor is for free, you just pay that little bit more aircraft hire time...
Costwise...in the S of England, you're looking at £100 / hr for a PA28, so £1200 in the last year (minimum cost), plus 1 hour with a JAR instructor, so £1235. Around £1000 in a C152. If you want to revalidate by the 'flight test route' or whatever its called, you'll probably end up paying for 2 hrs aircraft and 2 hrs examiner....but of course you may not do it in 2 hours if you haven't flown for 23 months.
If you're willing to go abroard you can fly a lot cheaper, but its probably not worth it unless you want to do a few more than the 12 hrs...
Cheers
EA