Hey, since you need to ignore these guys telling you to use a floor jack when you could be just standing up under a lift... here's a couple of links to tall transmission jack that won't completely break the bank.
SUNEX 7700B 700 lb. JACK:
http://www.sjdiscounttools.com/sun7700b.html
http://www.thetoolwarehouse.net/shop/SUN-7700B.html
SUNEX 7793A 1,000 lb. JACK"
http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=SNX7793A
The second one would be my preference if you forsee yourself doing a whole lot of trannies, simply because the foot-pump is much easier to use than the hand-pump style. It leaves both hands free to maneuver the ****** while you adjust the height.
That said, if I were buying one for use at home twice a year, I'd buy the first one. Either one is a HUGE step up from the stupid floor-jack style units. There's nothing wrong with them, but if I had a transmission to do and I owned a 2-post like you do... I'd sell a couple of tools until I could afford an upright ****** jack. Check and see what Astro Pneumatic and ATD have available, too - I've used a ****** jack from both of them in the past, and they were both pretty well made.
Believe me, you'll find all KINDS of uses for it. Anything that needs held up under a vehicle on the lift, will probably end up with that jack holding it. Dropping fuel tanks, crossmembers, etc.
There are two tools I think everyone who owns a lift should have. One is a tall ****** jack, and the other is AT LEAST one under-hoist stand:
Preferably two. You'll find a couple thousand uses for one, believe me. For somewhere between $50-100 ... they're well worth having. Go google "under hoist stand" and you'll find a zillion of them.
http://www.thetoolwarehouse.net/shop/OTC-2015A.html