I live in Canada where it's winter half of the year. You can get unlimited tanning at most gyms or tanning salons for around $20/month. It isn't overly expensive. Try to find a stand up bed. It's much better then a lay down bed. The problem with lay down beds is that they cause tan lines because you aren't able to move around when getting the tan. Stand up beds are much better all around.
In the winter, I go stand up tanning for 5-6 minutes 2 times a week. It leaves me with a 'summer' looking tan. Not overly tanned but not pale. If you want to be really tanned, go for 5-6 minutes 3-4 times a week.
The unlimited monthly rate is the best deal. That's what I would get.