Earlier quoted context omitted.
Solaris x86 vs RHEL is a no-brainer from a budgetary perspective.
Forgive my ignorance, but I haven't done the pricing for both. How do they work out?
RHEL is shockingly expensive for what you get. Either you do what they approve (in which case you won't really need their support, so you might as well be using CentOS) or you don't (in which case you won't get any support, so you might as well be using CentOS). But RH has the mindshare among developers; if you need to run something like Oracle on x86 then your options are RHEL or Windows.
Solx86 is free and of very high quality (far better than RHEL in package management alone!). But application vendors (e.g. again, Oracle) treat it as a tier-2 platform. So in many cases, it's just not an option.