Well, how much is the lot for sale for?

Are you basing this solely on what you can afford, or what you intend to make on it, or your target sale price? 

You can probably pay for a course when one of the sucker roadshows comes thru town, but it is a ton of money. 

Don't go for the cheapest (unless the price is lower because it is on sale), but also don't go for the most expensive. 

For example I would rather buy a property for a $100k discount that may have negative cash flow of $500/mo month for 3 years than pay market value for a property that cash flows $200/mo.

If your willing to do so, you can live in the casita and then rent out the main home and have your tenant pay the majority/all of the mortgage (depending on what type of deal you find obviously). 

We explained to him we would pay for probate and pay to fix up the house to get it rented.The lease is for 5 years but dissolves once we close.

Happy to pay for your time.  

We only needed to pay earnest money and a portion of the closing fees bring upfront investment to 12-15K.

If you have a great-paying, long-term tenant, a small discount can actually save you money in the long run.