Cheapo and reliable can be mutually exclusive. Most PSU's over 50 bucks are hybrid modular. 100% modular is kinda useless ... no sense having a cable you can unplug when if ya unplug that particular cable, your PC don't work.
Below 650 watts ya really don't save much money so it's sorta become the bottom level a self builder generallys elcts as saving $5 isn't a priority to the individual owener.
650 watt power supplies. For comparison purposes , the list below contains performance ratings (10 scale) at jonnyguru.com / prices as per newegg on 12/31/2010 and ones w/ double asteris (**) made it onto silentpcreview.com's Editor's Choice List:
Note: Just because you see a brand name on this list, never make the assumption that their other lines are of matching quality. Silverstone for example has other models w/ 6.0 and 7.0 ratings.
Originally there was a simple reason why lower wattage psu's were not modular. When modular power supplies were first introduced manufacturing costs were higher for the modular units and they commanded a premium price. Going modular meant higher prices. It wasn't a good deal for cost concious consumers on a tight budget.
I have the Seasonic X-650 Gold power supply. It just happens to be 100% modular. Even the main power cable for the motherboard is modular. However, I did not purchase it for that reason. I bought it based on competent technical reviews I read. Seasonic has a long term reputation for high quality power supplies that are consistently reliable and stable. It is one of a very very few brands that I usually recommend.
I do have a preference for modular power supplies simply because it makes cable management an easy task. I don't have to bother trying to deal with a bunch of extra cables that I don't need. Good cable management can help improve case ventilation, airflow, and cooling. A jumble of extra cables dangling every which way can reduce what othrwise would be excellent cooling. This is particularly true with smaller cases.