Paul is putting up Immortal Defense for sale at only $3 (original price $15) until this October 4th, which is probably the only time you can buy the game on the cheap and still receive full technical support from the developer. There is a lengthy demo that you can try out if you are on the fence about purchasing it. The game can't possibly be any cheaper than this, as BMT Micro charges $1.25 as the processing fee for every copy sold.

To get the discount, just enter BMCN000H7 in the discount code field on the purchase page. BMT Micro also accepts PayPal payments.