Here's a sample individually-sourced rig:
Evilbay regulator: $75 shipped. You can pay $25 to $300+, but for $75, there's no reason you can't have a really nice-looking, perfectly functional industrial (high) quality used regulator.
In order, from regulator to solenoid to needle valve to tubing:
Clippard 1/4 to 1/8 bushing (4CQN) $1.32
Swagelok 2" Hex Long Nipple (B-2-HLN-2.00) $5.03
Swagelok 1/8" street elbow (B-2-SE) $10.15
Clippard Mouse solenoid (ET-2-24) $28.56
Clippard Mouse mount (15490-5, 1/8" NPT ports) $7.29
Clippard Spade connectors (3831-1) $3.71
Evilbay 24V adapter $5
Swagelok 1/8" male elbow (B-2-ME) $8.82
Fabco-Air needle valve (NV-55-18) $34.75
Swagelok 1/8" NPT to 1/8" Barb (B-2-HC-1-2) $4.51
Clippard shipping: ~$24
Swagelok shipping: ~$10-20 (not sure)
Fabco-Air shipping: ~$12
Total: $240.14 (max)
Clippard fittings are very reasonable, but shipping is honestly offensive from Clippard.com. It'll be a bit difficult to source everything without going through the Clippard website, though.
Swagelok fittings are expensive, and you might save a bit on Evilbay, either for Swagelok or any other manufacturer's fittings (they'll all work fine). Shipping is reasonable but not cheap.
Fabco-Air nv shipping is on the steep end of reasonable, but you probably can't get it anywhere else.
The Clippard Mouse solenoid is good quality, and fairly cheap.
The Swagelok fittings can be substituted with any other manufacturer's fittings.
The Fabco-Air valve is decent quality, *definitely* better than anything from a prebuilt rig.
You can save some cash, maybe up to $50, by substituting Swagelok and Clippard fittings by Evilbay fittings.
On top of the listed price, you'll need at least one check valve, tubing, some type of bubble counter, and drop checker (recommended). Add another $20-30 for those.