Of course then you could get into RIMS or HERMS, but I have doubts about whether one could pull that off for less than $500 without finding some good deals on craigslist/ebay, or already having most of the necessary tools and maybe even some pieces of equipment that you could adapt for brewing.
price breakdown of the HERMS i built:
1- 1gallon S.Steel Bain Marie pot from walmart $8
1- 10-foot 1/2" copper tube $13
1- RTD Temp probe, grainger.com, $14
1- chineese PID, light-object.com, $32
1- 40A SSR, light-object.com, $12
1- copper 1/2" sweat:1/4"FNPT adapter $1
1- 1/2" copper Tee, sweat, $.70
2- 1/2" copper sweat:1/2" FNPT, $1.20
1- 2kW heater element, 8" long, $12
1- 1.25"x1" NPS reducing bushing (element screws into) $4
total: <$100
including electronic temp sensor and controller.
(not included- silver solder+flux, enclosure for the PID and relay/heatsink, some 12ga and 22ga wire and a few inches of 1/2" copper pipe i had laying around, and tools if you dont already have them. and of course, you need a pump.)
http://img.photobucket.com/albums/v239/ghost6303/beer/028c9f45.jpg
http://img.photobucket.com/albums/v239/ghost6303/beer/b9f4e1f7.jpg
http://img.photobucket.com/albums/v239/ghost6303/beer/7bbb3bd2.jpg