assuming you want heat + cooling so mid winter you can keep ales at 11-13C
your looking at
1) cost of fridge free to ??????
2) STC1000 circa £12
3) Box for the stc, £0 (icecream container) to £25 (hi spec ip67 abs enclousure)
4) £20 tube heater
5) upto £10 flex, glands,leggo brick connector strips, heatshrink etc.. and perhaps sockets if not wired directly..
6) upto £10 pc fan and dc psu to drive it (might find all u need in the shed or attic?? old desktop pc and old dc powerbrick??)
that gets you your basic brewfridge...
then you want taps,, @ £7.50-£45 each depending on what you go for, ebay branded ex pub dalex style taps are the cheapest shiny new us style perlick taps being the most expensive..
upto £5 on beer/gas line 3/8" OD ldpe tube for gas and keg connections 3/16" microline for restricting keg pressure down to a nominal 1-2psi at the tap point (upto 2m should restrict upto 15-20psi keg serving pressures)
co2 bottle 0-£50 deposit + £15 to £25 for a 6.5kg refill i use a zero deposit liquide air bottle at circa £22 per refill every few years.. charges vary depending on location, Monthly supply contracts are VERY expensive at our rate of use...
£30+ for regulator/s a single reg is probably all u need with Y or T splitters to share the same pressure over all kegs squeezed inside (all kegs at the same temp so the same serving pressure is probably what u need there )
http://www.kegerators.com/articles/carbonation-table-pressure-chart.php
upto £10 of JG fittings to connect and step up/down tube sizes to match taps and any microline used.
i would also look at investing in a pegas bottle filler too circa £70.... fill up pet or crown capped glass bottles with brite beer from the keg with a few weeks shelf life for distribution, taking to parties and events
freecycle is a good place to beg for a free fridge if family n friends cant pass on a 2nd use jobby.
hope thats useful...
happy kegging