Similar boat here , but lot of questions to help batter guide .
What are you intended ideas on why you need a spectrum analyzer , do you have the space for larger non portable ?
With the mention of the HP , that is kinda there .
Then what abilities do you have for diagnosing / repair , even if you find a working unit , and relative to your starting position - the HP .
You will find that , there is repair in your future , power supplies / electrolytic's .
I would venture to guess , the vast majority of used gear has issues somewhere in some function , unless you buy a refurbished unit - but now your looking at $$$ .
Before I suggest other options [ VNA etc. ] you want a tracking generator , either internal or external - like the HP T141 .
So already mentioned the Rigol 815TG , is minimal , but suitable for ham radio and near your budget .
Depending on what your intended wants / needs , something like a miniVNA Pro
http://miniradiosolutions.com/54-2/ may get you started , but I want both .
Something that can cover 2 areas of ham repair bench , a scope with FFT [ the spectrum analyze aspect is limited , but useful ] .
Putting a bench together , can be big / many devices .
So what gear do you have already ?