I've tested Microsoft TMG 2010 to load balance my two DSL lines and it works fine.
Can I expect the same level of results and security to be achieved with a less expensive firewall appliance?
I've used the following appliances with multiple IP uplinks that are not linked with BGP:
The netgear's worked, but it wasn't great. It had the basic ability to route different things over different links. The Watchguard was in a similar vein.
PFSense's also worked, and is a much more powerful tool. It's free, but you need hardware to run it on. I've got som 10Mb lines running on a Pentium II and it's been rock solid for more years than I care to think about (thankfully I have a stack of hopefully working spare RAM and hard drives).
TMG's worked really well in our environment because of its massive integration with Active Directory. But that's why we chose it, not its multi-WAN abilities.
So the short answer is: short answer yes with an if, long answer no with a but