The unit has been cleaned, but we can still smell the cat, and we feel the effects of the cat dander/urine. 

Consequently, if the seller would like to receive a reasonable asking price (along with the with limited fees associated with lease options, etc), they may have to sacrifice owning a primary residence until the option to buy their property is exercised.  

How will either scenario effect cash on cash return and IRR?  

Anyone know of the most cost-effective way to do this?

The most effective method for lead generation on the web is pay-per-click (PPC) advertising on SEARCH engines (google, bing).

The rest of the exercise is to offer what you can pay based upon the margin/profit you'll work for. 

If you're serious about wanting to get started, there hardly any more cost effective way to start your investing education.

On the other hand, if your buyers are serious about buying a home and want to have that "pride of ownership", you may have a winner.If your sellers are depending on the tenant exercising their option, you may want to educate them.

In effect, I had a partnership, with my parents.  

Consider sending in a 9 X 12 envelope as they can't miss it.Unless you're mailing many hundreds, this can be very effective as it adds value to your service, beginning with "heads up" this us what your house looks like now.