You don't need to be married.
My partner and I are not and she is a dependent on my ancestral visa. During the application all I had to do was prove that we have been together for at least two years, so as evidence we send photos, screenshots of facebook, evidence of travel together, also it helped that our house was in both our names. If you get marries just before you apply apparently it looks bad, as in just got married to get your visa, so the agency recommended we not do it.
We had absolutely zero issues, entire process took less than month, we used 1st contact visa and they where brilliant.
As long as your partner qualifies for a visa and you guys can prove two years history together you should be fine.
When you apply for EEA or Ancestral you don't need to have work lined up in the uK up, you only need to prove that you are looking for work and also provide your income in SA. I just send in emails that I received when registering on the job portals in the UK.
Costs for us 6 months ago,
Visas - £3000 (this includes NHS fees which you will pay on ancestry visas), if you go EEA its much cheaper.
Flights - R9000
Then just little things, like hotel accommodation and you need at least £4000 in your account for living expenses when in the UK but I would suggest more if you want to be comfortable try aim for £8-12k if it is just the two of you.
Everybody kept going on about how difficult it was and I was really stressed but after going through the process it was actually really simple, call 1st contact, they where really helpful. There are plenty IT jobs here, I was really surprised how many interviews I lined up in the first week I arrived.
as far as I understand that's where the financial problems start