Hi Chen,
There are some good suggestions above and I would agree with speaking to Spa Cycles to see what options they can suggest and I was also going to mention the Surly Midnight Special.
Another one to consider would be the Fairlight Faran frameset which is £599
It's a multi purpose, versatile, go anywhere bike which is built with comfort in mind.
Apologies as you might have to copy & paste the following because I’m having problems doing url links from my phone.
https://fairlightcycles.com/faran
It features the mounting points for mudguards & rack plus I would say that it's designed for comfort not speed as it's not a race machice with aggressive geometry.
https://fairlightcycles.com/faran-concept-design-notes
It appears to be a well thought out bike and if you read for example about the paint finish on the bike the do give the frame treatment to try and protect it which is done to varying levels by other compaies but sometimes falls short of the mark.
For me personally, and this is probably why my next bike will a Fairlight, one of the biggest appeals of their bikes is the fact that they provide two different sized versions of each frame offering both a regular and a tall version. Now although I've been cycling for a long time I've not had many bikes in that time and so I didn't know lots about bike fit and geometries when I bought one of my bikes. Despite the bike shop recommending the size to me I've never got on with it and discomfort problems are exasperbated with the longer the ride.
I've since come to realise that for my body shape and style of riding (primarilily everyday type riding with commuting, getting to shops and then occaisional longer rides including audax) I'm not personally a fan of a long stretched out riding position with a stem slammed low on a short top tube becaue I personally find it uncomfortable.
Fairlight have a principle called Fit Form Function but basically what the Fit part of it means is that they offer both a regular and tall version of each of their frames meaning that their bikes will provide a good fit to a greater number of people. The following video does a far better explanation of the idea than I ever could:-
View: https://vimeo.com/180866780
http://fairlightcycles.com/why-fairlight/fit-function-form
And you don't have to be an expert in order to figure out which frame size and version (regular or tall) is correct for you because all you do is select the model of bike that you want from the Fairlight website and then you can enter both your height and inside leg measurement and it will recommend which frame is best for you.
However if you look at there Instagram page depending on whether you want the frame right now it will depend on what size you want as to whether it’s available immediately. The reason being is that if you look at one of their recent posts it says that they are due to release an updated Faran frameset later this year and so they only have certain sizes left. You can see this on the recent post about the orange Faran build.
https://www.instagram.com/fairlightcycles/
Not that the following article is a review of the Fairlight Faran model but it's a Road.cc review of their Strael bike and it will give you a flavour of what Fairlight bikes are about.
http://road.cc/content/review/240016-fairlight-cycles-strael-20
The reason that I've recommended their bikes is because for me personally rather than the particular specs of a bike including the groupset, finishing kit etc., or discount percentage available the most important thing for me with a bike (which I've discovered over time) is the fit and geometry of a bike as well as the functionaility in terms of will it do what you want of it without being a hassle. For example is it easy to fit mudguards and racks to, does it take the tyre widths that I want to use etc..
http://www.cyclist.co.uk/reviews/2117/fairlight-faran-review
http://www.headsetpress.co.uk/fairlight-cycles-faran/
Depending on your intended uses this seems like a very versatile bike and for example I’ve seen a video of people doing a bike tour of the Western Isles in Scotland whilst towing surf boards on trailers using their Fairlight Faran bikes.
The short film can be seen here:-
https://www.pannier.cc/journal/beyond-the-north-wind-tour-headwindhaters-film-bikesurfing
If that doesn't show a bike being capable of anything then I don't know what does because I'd certainly not seen someone towing a surfboard on a bike before but then maybe I'm living in the wrong place.
However if the Faran either does not appeal then hopefully some of the other options above or perhaps something suggested by Spa Cycles might appeal.
I wondered if any of the Kona bikes such as the Sutra or maybe the Rove ST are available as a frameset only within your budget?
Good luck on the search for the right frame for you!
John