Your best bet is like this:
1. Get an unlocked 3G/HSDPA data card which will fit your laptop
. This will cost you $150 or so, not $1500.
2. Sign up for an unlimited data plan with one of the Mexican cell phone
companies (Movistar or Telcel; I think Telel is the one with good coverage in Baja
but check first). This will cost you about $35/months for "unlimited" data (actually, 3 gigabytes but that should be plenty). These are post-paid plans, so it could be tricky without an address. Use the first marina you check into as your address and pay immediately enough to cover several months service
3. If that doesn't work, then you can sign up for an AT&T international data plan for $200/mo for 200 megabytes/mo of data.
And away you go. You'll sometimes have 3G data, which is faster than dialup but slowe than broadband
. Sometimes you'll have Edge data, which is like a decent dialup connection. You will not get a signal everywhere (Los Frailles, to name one place, has no cell phone
You can improve the range by putting a cell phone
repeater or antenna/amplifier at the masthead; better yet a fixed high power marine
GSM phone like the Ericsson W25, which is what I intend to put on my boat. But that's a bit like gilding the lily; as long as your coastwise and can tolerate being without coverage a couple days here and there, you'll be fine with the regular data card.
When you are in marinas, you will often have free WiFi
(like in La Paz), so you'll be using the cell phone system not all the time.