I helped a friend and his Thai girlfriend apply for one a couple of years ago and it was granted in less than a month, so obviously there are variations in timescales.
Basically, yes. In Australia they have a term 'de facto' which unlike the UK 'common law', is a legal status, so you can apply for what is called a partner visa, even if you are not actually married, but are in a provable 'de facto' relationship. The United Kingdom does not recognise common law marriage. That said, the rules in the UK may have changed, I've been out of that loop for some years, but I do believe they have a legal partnership status now. There was certainly a point in time, back in the 90's, when if you were in a hetrosexual relationship and you could get married, i.e. you were not barred from doing so because you were already married, then to get residence status for your partner, you had to marry. I know that because it happened to me. The irony was that if you were already married, but not divorced, or you were in a same sex relationship, so in both cases you could not get married, then you could apply for residential status for your partner. This was before the The Marriage (Same Sex Couples) Act of 2013 came into force in the UK in March 2014.
I did one for a friend of mine and his partner a couple of years ago. I live in Thailand, as did they, so the application was submitted from here. I believe the cost was about AU$ 7900 with no agents fees, as I did it. If you can work your way around the bureaucracy, and the not user friendly online application, it’s doable yourself.
I always type it, using the online TM7 word document and then print it. As a consequence it is completed in black and that has never been questioned. That is at Hua Hin immigration.
I transfer from the UK to my Kasikornbank account using Wise and they do not charge a fee. Previous international transfers, prior to using Wise, incurred a 500 baht fee, so it’s another saving.