We didn't use
BB but we have done prospect screening on our Dtb.
We figured out we couldn't afford to do the whole DTB (30,000 records) but we could afford 8,000 based on the information we wanted. (birthdates, financial info, prospect ratings, etc.)
We based the criteria on recency alone and were able to get donors in the past 2.5 years. I would avoid doing it on giving level because you miss out on donors who are giving WAY under thier potential. You may be surprised at how many $20 donors are very wealthy. You may never get them to make big gifts but consistent long term donors regardless of giving level make great planned gift prospects (and those with wealth give BIGger planned gifts).
My other advice - have a plan for what you will do with the data when you get it. Special mailings to prospects asking for larger gifts that you haven't included in your budget? Special invitations to prospects to cultivation events you have yet to plan?
Prospect data has a lifespan - you can't sit on it for a while then do something with it. Make your plans now BEFORE the screening based on what you can afford (CEO/ED to phone top 50 prospects - invite next 200 prospects to event - mail to next 500 prospects, etc) If you can't afford to do anything different in your program based on the results then the money will be wasted.