The cheapest way is to purloin some old fluro fittings & purchase black light [UV] tubes from a lighting supplier.
In fact with the fixtures you can pick them up from a local savage yard or I believe they are fairly cheap @ Target or one of those type shops.
At least from Target or a major cheap lighting outlet, you have a warranty that they work.
There are cheap Import fixtures from China these days, available in most sizes.

TOI TOI TOI
CHOOKAS

[May you always play to a full house]
Hear the lights & see the sounds. 

Most blacklights are 4' and these are generally available, if you're in Perth I can give you some fittings and sell you some tubes, if you're anywhere else Jaycar sell a low cost tube, not as good as the name brands but fine for general use, a higher power unit is a 400w unit, costing around$100 which fits into any 400w mercury vapour fitting.Fluoro tubes switch on quickly while the 400w units take some time to build up.

The Jaycar ones are poor when alongside the philips so save your money and buy the philips or other brand name ones if you want effective blacklight.

The 4 foot 40 watt ones are almost as effective as the 400 watt ones and don't have a warm up time. Six 4 foot units will do a medium size stage, just make sure nothing masks the distribution.

Na one of the biggest factors when using Black light blue {BLB[UVA]} is with your costumes & sets. These days there are a myriad of dyes, makeup & materials available. I'm sure in Melbourne you would have Halloween shops, which carry them all in stock.
Also one thing to think of is if your using 'black Ducks' {techies in black garb] try & suggest they use 'Head & Shoulders', as dandruff on black clothing will show up. also a lot of dry washing powders will also react to UV [BLB] & you might be able to also use for a UV effect.
Also if you fossicking thru a Salvage yard, be careful not to buy any industrial UV equipment, especially any UVB or UVC, as these are the in the harmfully short wave UV spectra. There again even the safe UVA longwave will promote ageing with prolonged concentrated over exposure.
BLB is a similar process as 'Woods Glass' used in UV discharge theatrical lamps.
Interesting site;- http://www.uvgear.co.uk/product/uvbulbs.htm
If you chat to a local Lighting & globe wholesaler, a few comps does work wonders. You might find they have package damage tubes or shop soiled fittings even discounted lines, you could take off their hands for a song.

TOI TOI TOI
CHOOKAS

[May you always play to a full house]
Hear the lights & see the sounds. 

Thanks everyone for the advice. I've been wanting some small, but decent blacklights for a while now - for puppetry - but haven't been able to find some good cheap ones. In Melbourne, there are a few lx companies that sell them, but they are quite expensive; especially as you need to buy more than one for them to be effective.

I did have a look at Jaycar, but based on David Ashton's comments I'll look more closely at something from Philips first.

Thanks Joe for the advice on costuming; but alas, you are too late! I've done blacklight before... well, technically a light curtain, which isn't the same, but it requires the same costuming. So I'm all set in that department: we have several velveteen costumes made with hoods, tops and pants... And I definitely won't be looking at anything industrial - I wouldn't know what I would be looking for!

Thanks all!

Fun puppet patterns to make at home! Puppets to buy at
Puppets in Melbourne

sheezaright Na!
You can get the Small BLB lights the size they used to use in Banks for secret signatures. they are cheap enough!
These days I'm always late, but not when it comes to cues?
Having been born backstage on Tyneside in Geordieland. Maa Mam allegedly had just taken the finale walk down & I popped out after the final curtain call apparently. I have never missed a cue ever since - well that I wish to own up to anyway!
Supposedly the event took place in the ambulance outside the Stage door, at the plinth of the stature of my Great Uncle Joe on the corner of Westgate Road Newcastle Upon Tyne.
So it has't be in the jeans?

TOI TOI TOI
CHOOKAS

[May you always play to a full house]
Hear the lights & see the sounds.