A few years ago I was able to use SMAART from rationalacoustics.com and was very impressed. Unfortunately, it is way over my budget. I was hoping there might be some more affordable solutions.
First let me say that the principal of Rational Acoustics is a friend of mine, I have beta access to their product, and I think very highly of SMAART 7. It is the easiest to use of the major multi-channel FFT measurement programs (i.e. SMAART, Systune, and SIM3). I also own Systune. Now that disclosure is out of the way, answers.
The best bang for the buck mult-channel fft analysis program out there is arta, but arta is not for uninitiated. It is very powerful but requires a deep level of understanding.
Before you read any farther in my answer, I suggest you read an article I edited for Live Sound International magazine called The Devil with your RTA. Digest that article as much as possible, and then consider what you are asking the software to do. Come back here with a followup and I'll help you think it through.
The tl:dr is this: "Real Time Analyzers "RTA" will tell you the level for each frequency of sound that arrives, but won't tell you when each frequency arrives relative to the others. The latter is extremely important in aligning professional sound systems and extracting the most performance from loudspeakers."
heard good things about TrueRTA but I can't provide more info than the one available at their website. Then again, if you tried SMAART (I can tell you it's an unanimous consensus that SMAART is the best tool out there for venue tuning, both in Portugal, in UK and NZ) you know that there's more than a high resolution spectrum analizer but also frequency over time plots, average graphs, multichannel input, etc.
There's also Klark Teknik DN60 (now I hear there's a really swanky 6000 version) I know it used to cost about 2000€ I think but maybe you can eBay it pretty cheap or speak with a local sound company looking to improve to smaart or the DN6000?
Again, as asked above, what exactly did you like on Smaart? because if you just want to have something on the corner of your eye for reference you'll probably get away with trueRTA. Get yourself a nice 1 channel converter and a relatively nice microphone. I gather that if you said smaart was out of the budget you won't be looking for B&K's mics.