From your perspective, I can see it being quite awkward without there being a nearby ferry. Its not nearby for me, but its at least at this end of the country.
On last year's price, the freight crossing from Tilbury is ?415 return. That's a Tuesday, Thursday and Saturday crossing to Gothenburg, including berth and meals. Two day crossing. HOWEVER. The part I'm not happy about is that freight traffic get priority. That means that if its a busy day and they're packed, we could loose the crossing to freight, despite booking in advance
If that happened, it could be possibly to go down to Dover for a crossing and drive it, but it'd be winging it all the way.
The alternative in planning to drive the whole way. That'd be a ?72 return with Speedferrys to Boulogne (55 minute crossing). Then a two day drive up through France, Belgium, Germany, Denmark and Sweden. Obviously, we'd have to sleep somewhere on route.