Which Used Treadmill Should I Buy?

I have a membership at the local YWCA so I can use the fitness room for the weight machines, treadmills and ellipticals.  I find it very had to get over there … I hate to add even the 10 minutes to my morning workout schedule.  Why get up any earlier than I absolutely have to?  So I have some hand weights and DVDs for cross and strength training and, up until last week, a treadmill.  I used the the treadmill a lot last winter when I was still walking, but by April I was running and outside in the lovely spring air.  I only just started using it again when the temperatures were below freezing and the road sides were full of snow.  During a run last weekend it started grabbing and stopping every couple of seconds, so I had to stop my run for fear of hurting myself. 

Anyway, I need a new treadmill for those days I just can’t get outside because it’s too cold/hot/wet/dark.   But I don’t want to spend a lot on it as I don’t plan to use it that much and already spend money to use the machines at the Y.   I belong to a local mothers club with about 450 members and I sent an email out to the group asking if anyone had a treadmill they were interested in selling and got the following responses:

HealthRider 5500xi
$200
5 years old

Life Fitness Essential FT6
$700
4 years old

True Fitness 450
$ thinking about it
Bought used 3 years ago

Plus one other unknown treadmill belonging to the neighbor of a member

So – what which one should I buy (if any)?