I'm glad to hear you got the issue fixed.
If you watch the popular auction sites you might find a used Autel MaxiDAS DS708 on sale for a price you can afford. Of course determining what you can afford sometimes means putting a value on your time. If you can rationalize that finding a problem 3 times as quickly without replacing 5 parts that don't fix the issue allows you spend 2x on a diagnostic tool versus what you want to spend, that might raise your budget a bit. The DS708 should do everything you would ever need for the 1999 Explorer. Then if you need to update it at a later time, it runs around $400 to get another year of updates.
-Rod