IMO online and cheap usually do not coexist for corals/fish. So far, I've only seen fishofhex sell relatively cheap corals but I haven't done any serious searching for online vendors. If your location is right and in the UK, most of the reefers here are US based so we only have experience in the US market.
Your best bet is hunting through your local reefing groups on facebook and finding the local importers. DFW, for example, has an airport that can support international freight so there are roughly 6+ importers I'm aware of with 3-4 that i've seen have very very reasonable prices.
You can also find local reefers as well who are either trading or selling their home grown frags.
LFS stores are hit or miss for me in terms of quality and cost. Usually its like 30-50$ for a frag of anything and often times their frag tanks act as "trading posts" for local reefers and are subject to a higher risk of getting pests like aptaisia or one of the harder to control algaes (bubble, cladophorisis, etc)