Pick almost any date for MAN-LIS and you will get a much better deal with TAP Air Portugal than the " low cost" airline BMI Baby (esp if you have bags to check in !)
Like any other transaction shop around, & like Shed says never assume a LCC is always the best option.
Having mentioned TAP, I wonder if they are going to give the route any publicity ? Seen very little info about the route apart from the MA web site.
With TAPs South American network it also weakens the case for a BA/IB Madrid service, more so than the RYR flight.(IMHO)