Nothing beats the feel of those heavy B-3/M-3 waterfall keys and the growl of the tube amp through a real leslie. Someone should sell a little kit that burns hammond oil so you can get the smell from the emulators!
If you are starving musician....you can get away with getting that sound for under a few hundred bucks if you REALLY want to get a REAL Tonewheel sound.
Many people get old beat up M-100's, M-3 and L-100 spinets for free and Cut them up for portables.... but they still weigh a ton!! (PS..please don't cutup a perfectly good Hammond Tonewheel Organ) Hammond tonewheels were built to last hundreds of years and never go out of tune, with a little help from Hammond Wiki and some Hammond oil (never use anything other than hammond organ oil...and maybe a slight mix of lighter fluid if the wicks are gummed up and the tone generator doesn't turn when you first get it)....read
http://www.dairiki.org/HammondWiki/ before picking one up so you know how to lock the tone generator and reverb down and how to test it...Hammond organs can kill you hours after they are unplugged from the power stored ....know what you are doing!!
But with a little work and a hundred bucks for parts, oil and gas to pick it up (you can add foldback to spinets with a kit) You can have an awesome home made Porta-B!
Problem will always be the weight, those manuals weigh a ton and of course the Tone Generator and amp weighs a lot too, Not many places you can still play where you can get even a Chopped Hammond in there.
But...another cheap and even better option is sampling a real Hammond organ with an old rackmount so you don't have to bring a computer to a gig, lots of people on the web sell Hammond organ samples of many different B-3 type organs, Every Tonewheel Hammond organ sounds different depending on it's age, Caps, Tubes, amp settings and tone cabinets/leslie mods. By Sampling a bunch of different B-3,C-3, A-100 and even the old A and D's with the large tone generators for the full bass, you have a much better range of really good REAL organ sounds with that nice tube sound. Personally I think the samplers sound better than any of the Hammond tonewheel Emulator keyboards, and you could get one used for a couple hundred bucks. Something with as many voices as possible since the Hammond Tonewheels are unlimited polyphony and to play them the same as a B-3, you don't want long full sweeps being cutoff too much.
Check out Hammond organ Samples on youtube, lots of examples there