Bite the bullet and spend a bit of cash. I got a Eleaf iStick 30 and a Kanger Subtank mini RBA. The tank holds 4.5ml juice, and the battery lasts all day. It has variable voltage up to 4.5 volts through a 0.6 ohm atomiser. The Atomizer itself is rebuildable using premade coils at a couple of quid for 10, and pure cotton, again a few quid for a year's supply of wicks. It gives enormous clouds of vapour, and is very satisfying. I currently use 6mg juice.
On top of that I mix my own juice. Online you can buy enough nicotine base to last forever at £18 for 250ml. I use 8ml to mix 100ml of juice. 250ml of PG costs about £6, as does Aqueous glycerine, and pure flavour concentrate costs less than a fiver for a bottle.
At my mix rate of 6% nicotine and 15% flavour that 250ml bottle of nicotine will make 31.25 x 100ml bottles of juice. Each 250ml bottle of PG and AG will make 6.25 x 100ml, and each 20ml bottle of flavour concentrate will make 2x 100ml bottles, with a secondary flavour that I use making up the rest at 4x100ml bottles per 20ml concentrate.
Therefore I can make a 100ml bottle of juice costing 57p for nicotine, £1 each of AG and PG, and about £3 for flavouring. ... less than £6 for 100ml.
T