I'll through my 2 cents worth of confusion into this. I have several "old" (circa 1920s - late 1930s) planes (#4, two #5s, #6 and #7). The #4 Stanley I inherited. Both #5s were bought on e-bay for a total of $25 delivered. One is a Stanley and one is a Marshall Wells. The #6 Stanley was bought on e-bay "buy it now" for $35, and the #7 was bought at a Midwest Tool Collectors Association (MWTCA) meeting for $45. My most recent additions (over a year ago) are a Lee Valley Low Angle Jack with all three blade bevels and a Lee valley scrub plane.
I use all of them a lot in my projects, and consider all worth what I spent in time and money.
If you really want to learn how to use hand planes, then buy a $25 or so Jack (#5) off craigslist, e-bay, or better yet at a MWTCA meet. If buying from e-bay, look for one that has pictures from all sides. Disregard any that have a crack near the mouth of the sole, are covered in rust, or are incomplete (i.e. missing/cracked tote, cap iron, adjustment lever). Preferably one that looks like it has recently been used (little red rust on sole) and preferably one that hasn't just had a recent paint job. Then go to Home Depot and buy a couple of cheap 2" Buck Bros irons for it. Go on line or attend a class/workshop and learn how to sharpen the irons and fettle the plane. After this exercise, you will most likely know how to use it, how much you expect to keep using it, and what to look for in your next purchase, all for less than $50.
If you want to get a plane that works like its supposed to (takes out of the equation the unknown of whether any problem is plane or your technique), want it to give you the gossamer shavings the first time, and think you will use it occasionally, buy a Lee Valley or Lei-Nielsen. Be aware if you start at the top, that is where your expectations will be for any future planes.
Either way, good luck.
Go