How much damage can a grow-op do to a house in 3 months?
I have experience buying similar houses.  Basically GrowOps have the following issues:


Electrical redone to support lights and equipment
Ventilation rerouted through places where it shouldn't
Plant and smoke smell throughout the house (if they are growing most of the time there are lots of people smoking).
Moisture inside drywall


In your case you are lucky.  Doing a GrowOp in the basement offers access to ventilation and electrical without having to radically change anything.  You can simply add a circuit to breaker or tap into another and pull it once you are done.  Ventilation can go out basement windows/doors.  

If I were doing a full inspection the first thing I would do is inspect the area for how they were getting their electric.  I would definitely open the panel to make sure there was no stupid add-ons that weren't done by an electrician.

Next I would be looking for fresh drywall/paint/mud.  If they had to open up walls for ventilation I would be weary that the inside of the walls were OK.  At the same time I would make sure I smelled the house minus candles/scenting.  I would open up the house and then keep it closed for a while and do a smell test.  Getting smoke/pot smell out of drywall can cost a fortune.

Last check the attic.  A lot of pot houses I have inspected vented into the attic.  It doesn't mean you don't buy the house but you need to figure out the damage done in attic and how much it is to fix.

Given your situation I would mainly be concerned about smell.  Check everything else out and simply subtract any issues to already low price of home.



Special Note:  For anyone legally doing this I would offer the following advice (note that this is generic and obviously won't work for all situations):


run new circuits for this usage.  You will probably need a couple of 20A circuits for even a smaller operation.  If you are in a basement this is usually super easy.  Without a basement I would suggest using armored wiring for temporary lines or just opening a couple of walls.  Do not overuse your current circuits.  This could cause a fire or burn out a lot of outlets.  No amount of goods is worth burning down your house.
for ventilation you will need at least one large run or possibly two medium runs with an induction fan for each.  It would be best to pop these right out windows but this may effect neighbors or draw too much attention.  Using flexible venting through attic and directed out gable vent would be a good temporary option.  
everything you are growing should be encapsulated in plastic.  If it were my house I would have a tent that housed everything with the ventilation the only permanent opening.  I would then tape plastic sheeting over every surface in the room where it was growing. So tent and every wall is blanketed with plastic sheets. 
I would run a dehumidifier outside of the tent.  Possibly one in the tent too but this would depend on readings and condensation I was getting in the tent.  
I would have smoke alarms and carbon monoxide alarms checked and plentiful.