At Mouser.com, you can get 1/2 lb. of Kester "44" solder in an eutectic mix (Sn63/Pb37), with a 0.025" diameter, for only $8.50! That's a better deal for a much better solder. You save $5.75, and you get the best solder available for DIY electronics.
Now, if you buy the 0.031" diameter Kester "44", then 1/2 lb costs only $7.80! That, of course, is quite a bargain. The only drawback here is that the 0.031" diameter is a little bit harder to work with (too thick). But if you must save $$$, this is the one to get! It's very, very cheap!
Here's Mouser's part numbers for these eutectic solders:
Kester "44" with 0.025" dia: 533-23-6737-18 = $8.50 for 1/2 lb.
Kester "44" with 0.031" dia: 533-23-6337-27 = $7.80 for 1/2 lb.
http://www.mouser.com
NASA uses Kester solder for their critical electronic applications. So it is highly recommended.
Another point to remember: That easiest way to avoid cold solder joints is to use eutectic solder (63/37). Eutectic solders do NOT have a pasty state. They go from liquid to solid instantly. That assures you a fine grained, solder joint that works perfectly every time.
Eutectic solders melt at a slightly higher temperature than 60/40. Thus, you do need a hotter soldering iron. However, a 25 watt iron with a tip temperature of 750 F or slightly more will be enough.
BTW, silver solders with Sn62/Pb36/Ag2 mix are also eutectic solders. This is a great solder also. The problem here is that Kester does NOT offer this solder in 1/2 lb roll. You must buy a pound for $26.80 in the 0.025" diameter (Mouser part#: 533-24-7150-18).
Cardas Quad Eutectic Solder...
That's the solder I use, and it is available from Michael Percy. It's a great solder that gives perfect solder joints every time. I never get a cold solder joint with this superb solder. The "quad" part of the name refers to the 4 metals used in the solder: tin, lead, silver and copper! The cost of this boutique solder is $21.00 for 1/2 lb and $11.00 for 1/4 lb at PercyAudio.com! Cardas.com recommends a 25 watt soldering iron with a tip temperature of 750 F for this solder.
http://www.percyaudio.com
I also use the Kester "44" mentioned above. In four decades, Kester has perfected the "44" and made it into a very fine, reliable solder. Use it with a 700F soldering iron (minimum). Hightly recommended for newbies!
Good luck with all this info!