For C-41 "passive" solution can work especially during summer (when there is less difference between ambient temperature and bath temperature which is 38 °C, or °37.8 depending on who you ask).
The only temperature-critical bath is the first, developer, both for C-41 and E-6. For the subsequent baths 33 °C - 39 °C is fine. Developer in C-41 lasts only for 3:15 (standard time for first treatment) so it's possible to use a "passive" method if you use a plastic tank which you preheat accurately. With E-6 it's not the same, my standard time for first developer is 7:30, an "active" solution works certainly better.
You can search APUG for "fish tank heater", you'll find solutions. They are good for the "other" baths. They need a "modification" for the first bath as they will not arrive to 38 °C, you have to break the temperature limiter.
You can find cheap Jobo machines that only keep chemicals in temperature. An example:
http://cgi.ebay.de/JOBO-TBE-Temperi...der_Entwicklungsmaschinen&hash=item2eb6b20d15
You can get one of those above for 40 or so plus shipping. I think it would be ideal for you.
The step forward would be rotating processors. CPP-2 are probably the best. CPA-2, CPE-2 are also relatively recent. Some older Jobo models are also available on auction sites. Highly recommended for colour work.
Somebody recommends DIY, you'll find some solutions faintly sketched.
Another ready-made solution is a common food-warmer (better if one of those which can be filled with water) but they tend to cost more than the Jobo above.