The most expensive item will be your mortgage.
As a rough guide, your current mortgage will be around £600 a month per £100k of loan – so if you have a £150k mortgage you will be paying £900 per month. To stand a chance of getting that mortgage, you will need a 10% deposit (£15k on a £150k property).
And the killer requirement (on getting the mortgage), multiply the higher earners salary by 3 and add the lower salary – you might be lucky to find a mortgage provider willing to lend this much. i.e if one of you earns £20k and the other £15k, that works out at £75k.
Best stay on friendly terms with your parents for the foreseeable future.