Just make sure you don't need a "slim" type of PSU - as these are the "regular" sized ones.
I wouldn't suggest going any cheaper on a PSU - just due to the fact that a power supply is your most important piece of equipment (since it powers your system). A bad/poorly made one can blow your components.
By the way modular means you can disconnect and connect any power cables you don't need. Non-modular means all the power cables are already connected and you cannot disconnect the unused cables.
I would suggest a modular one - as to make your case a little tidyer.