Hi, I too have built the Tony Messina bat detector and it's an excellent little tool for the price. If you'd like the benefit of someone else's experience the following parts work well, all from Maplin
http://www.maplin.co.uk
Description--------------------------PCB Comp No.-----Maplin P/N-----Price
Plastic Case with 9 volt battery clip-----n/a-------------ZB17T--------£3.29
40KHz Transducer----------------------n/a-------------HY12N--------£4.99
Binary Counter HCF4024BEY------------IC3-------------QX13P--------£0.86
High Impedance Ceramic Earphone------n/a-------------LB25C--------£1.99
10K Ohm PC mount variable Resistor----RV1-------------UH03D--------£0.19
LM386N-1Low Voltage Power-Amp------IC1&IC2---------UJ37S--------£1.06
3.5mm, 3 circuit stereo phone jack------n/a-------------FK20W-------£1.06
470uf, 16v electrolytic capacitor--------C4-------------VH46A--------£0.23
10uf, 16v electrolytic capacitor x 2-----C2 & C3---------AT98G--------£0.22
0.047uf Mylar capacitor----------------C1--------------WW20W------£0.08
220uf, 16v electrolytic capacitor--------C7-------------VH41U--------£0.11
0.022uf Mylar capacitor x 2-------------C6&C9---------WW19V--------£0.14
9v battery PP3 clip with wires-----------n/a-------------HF28F--------£0.29
150 Ohm resistor 0.125w----------------R1-------------M150R--------£0.09
1K resistor 0.125w----------------------R2-------------M1K----------£0.09
220 Ohm resistor 0.125w----------------R4-------------M220R--------£0.09
Carriage (Maplin)----------------------------------------------------£2.50
Maplins Total-------------------------------------------------------£17.28
You won't need a detuning coil as described in Tony's instructions, but you will need to wire the phono-jack socket correctly. I had a problem getting the soldering of the jack right and I'll post some pictures of the circuit board fitted out for the UK using Maplin components if people need the help.
Tony's website
http://pw1.netcom.com/~t-rex/BatDetector.html has all the documents and tips you'll need, and personally I'd go for the enhanced detector, the list above is everything you'll need but the board. The PCB can be bought direct from Tony using PayPal, but if there's enough interest I can stock it in the UK on his behalf and reduce costs all round.
We're also looking a keeping some kits of components and boards in stock too, so if you'd like either a board, or a board and a set of components then e-mail me direct.
Lee