Economics/RentOrBuy

With that said,
 * Renting a house = 50 gp/month.  Buying a house is a 50 gp discount per month.
 * Annualize the discount and divide that by the discount rate (default 10%).  50 gp x 12 = 600 / 0.1 = 6000 gp.
 * If the house is meant to cover this for 5 PCs then make the house worth 30,000 gp.

The creature is as tame and obedient as any other pet from the pet store (which is to say, mileage varies, but unlikely to attack with intent to harm). Move the price/level down one for a feral, and up one for a trained, combat-ready specimen.