If you're seriously considering spending upwards of £20k on an SSTR, presumably you have considered which airlines you would then target? I ask because virtually no-one is recruiting, and there are plenty of type rated and experienced pilots who are out of work at the moment.
An SSTR is a very expensive gamble at the best of times - and right now the job market is awful. If you still have an instructing job, I'd suggest you're better off hanging on to that and continuing to build hours that way. When (eventually) airlines start to recruit again, turboprop operators in particular are more likely to be impressed with 1000hrs P1 SEP than a 737 rating and no line experience.