If you are willing to use an app that doesn't work as well, has less support, and you aren't willing to pay $1 or less (which is what I imagine the OP's app costs), then go for it.
Aside from a few things (apache, php, mysql, linux), I generally use open source in the beginning when I'm trying to cut costs..but almost always end up going with a proprietary solution when I need to get serious about it.
Open source has it's place, but it's not the software utopia that the community claims it to be.
Security is the #1 misconception. The claim is that it's more secure because there are "more eyes looking at the code".
If you look at any major open source project, there is usually a core set of developers that actually make any set of changes to the main core. Combined this with the fact that 90% of the project users don't know enough/anything about coding to make any changes and the odds of getting security changes fixed are probably around the same as a proprietary application.
Most users also don't update (proprietary or open source)..contributing to insecure software. I can't tell you how many Wordpress installations I've seen out there that are using sub 3.X/insecure versions.