I heard a rumor that once a westerner has a land lease, in addition to the purchase of the lease, there would be an additional cost of 10,000 Baht payment to the owner—it wasn’t clear that that amount was a monthly payment. Is there a site that covers the ins and outs of the process for aquiring a lease, including advantages vs, disadvantages? If my opening statement were true, why would someone want to enter a lease when they could simply lease a house with an established garden for somewhere around that 10,000 Baht figure?

You are bound only by the terms of the lease.  And you do not purchase a lease, you simply set terms with the owner, have the lease written up as such, and sign, paying only what you agreed to pay.