Buy once cry once. You don't need the best of anything, but it's vastly easier to learn the trade with proper tools than it is with poor equipment. I understand the budget and expense is a lot to swallow in some cases, but that goes along with Stacy's advice - take your time, you don't need to purchase everything at once, or be able to make every kind of knife under the sun from the get go.
A proper tool arm 2x72 grinder can be had with variable speed on 120v electricity for <$1000 these days, and is lightyears beyond any 1x30, 1x42, 2x48 grinder out there. You will use it on every knife you make, regardless of the type, size or style. Mastering the skill of grinding will reduce the amount of work you have to do by hand to finish a knife and will translate into other areas or use of other tools like a disc grinder.
I get the desire to make a knife and to do it now. I think you're better off saving the $200 you might spend on an inferior grinder and using files and a guide to do it, if you have that desire. You will never regret investing in a decent grinder setup, because even if you decide this isn't for you, you'll be able to sell it for close to what you put into it.
But a lot of the learning process is trial and error, no matter who has instructed you or how much you've read, and the lesser grinders simply throw more variables into that feedback equation that make correcting your mistakes harder to diagnose.
ETA: To be clear, it isn't about what you spend on a grinder, it's about what you get. Whether it's a kit, home build, or a $3,000 top of the line commercial product: if it uses tool arms, 3/4 wheels, tracks true and steady, runs 72" belts, and has variable speed - then you've got what you need whether it cost $300 or $3,000.
