I'd personally recommend the RC1a, I've built one and got the bits for a second. I've had only minor issues with this which I've yet to try and fix becasue it still works, kinda.
Parts wise, I too live in the UK and ended up buying ALL the bits from DigiKey although the +6V boost chip didn't work and had to be re-ordered from Farnell. This cost me a lot. An awful lot. £155.96 not including what ever UPS tried to rape me for for shipping, VAT, customs and the fee collection fee (this is for 2 wavebubbles with both battery options). The main problem with buying from DigiKey is that despite having a UK site they are firmly an American company so you get socked for the above mentioned fees by UPS. I've tried to sort out a Farnell friendly parts list, but there are a few items (the power switch, the PLL chip off the top of my head) that are impossible to find in the UK. I think the WB2010 has a better parts list for UK ordering but there are some concerns as you've noted.
The other thing will be the VCOs and RF amps. I bought everything from minicircuits.
4x GALI-84+ RF amps
1x ROS-1300+ 400-1300MHz +5V VCO
1x ROS-1700W+ 770-1700MHz +12V VCO
1x ROS-2500+ 1600MHz-2500MHz +12V VCO
1x ROS-2700-1819+ 1300MHz-2700MHz +5V VCO
Total: £139.31 inc shipping
This was mainly pricey because I was buying two sets, the standard +12V VCO wavebubble and my unmade wide-wide-band +5V VCO wavebubble. Alot of the quoted prices can be cut in half or more through thrifty spending on a single wavebubble. A wavebubble is not a sound investment if you simply "wanna blk dem mobbies!!" etc. but they are DAMN fun to make and exceedingly satisfying to get working.
As you are in the UK I hope you are aware of the fact that while we are allowed to own a wavebubble legally we may never turn it on. If you were to do so and get caught
then OfCom would get involved. And large (multiple 10s of thousands of pounds) fines would be payable.
I bought mine from aqisnotaliquid nin a similar thread to here
and was most satisfied.