get a good one!! blade needs to be tight and well supported. eclipse make a realy nice heavy one. personaly i have a bancho?? its realy nice very strong and realy tensions the blade whilst not letting it twist. cutting 2" solid mild steel rounds is a 20 minute process with it.
if the blade can wobel after tensioning throw it in the bin. dont skimp on the blades either. a decent quality blade makes life a lot easyer. stick to bimetal blades not fully hardened as a slight twist and the hard ones shatter easly. stick with 12" blades too, i have never understood why 10" are offered, generaly on the average stroke the last inch - 2" of blade are not used, a 12" blade has a lot more life in it for very little extra cost!! also keep a small stock of blades in a range of tooth forms and swap them just like u would any cutting tool to suit the job at hand.
then mark all the way around and follow ur mark from both sides. done with care its easy to keep even long cuts accurate to under a 1/16" and a 1/32" is very possible. also dont go to fine on the blade, just results in a slower cut in thicker sections at the expense of getting tired and frustrated on your part.
also think of all the money your saving on that gym membership!!