A challenge... ?

I wonder if anyone has the time (!) to help.
I'm looking to book a flight for my son. Using miles. In Economy. I have enough miles for most eventualities.
He has to go to Vancouver from LHR; he then needs to go to Singapore, back to London. Dates are a bit flexible, but leaving LHR around 15 April, week in Vancouver, week in Singapore. Or so.
He has a budget of about £650. I don't believe its possible to do this trip, at that price, assuming all miles and charging for taxes/charges. However, I don't know about US taxes/charges. Neither have I ever booked with miles on Delta - I nearly always go East not West from LHR. So, I'm unfamiliar with US routes internally or from there East.
So far, I think the best route is LHR - Vancouer RTN, via Seattle. So a Delta hop from Seattle rtn Vancouver. (Delta or VS re LHR/Seattle rtn ? - miles are different, but are taxes?). I've no idea what the taxes are for the Seattle/Vancouver Delta rtn hop. This takes him back to London. I reckon this costs about £350 (290 tax for LHR/Seattle, the rest a guess for Delta Seattle/Vancouver)
Then LHR - Sing rtn on Sing airways - don't know the taxes for this. But I reckon it will be about £ 400.
So £750 total which is not too bad.
But it seems a long winded way to do it. If anyone has a better idea, I'd love to hear it. Please ignore if you have better things to do.
Thanks very much
I'm looking to book a flight for my son. Using miles. In Economy. I have enough miles for most eventualities.
He has to go to Vancouver from LHR; he then needs to go to Singapore, back to London. Dates are a bit flexible, but leaving LHR around 15 April, week in Vancouver, week in Singapore. Or so.
He has a budget of about £650. I don't believe its possible to do this trip, at that price, assuming all miles and charging for taxes/charges. However, I don't know about US taxes/charges. Neither have I ever booked with miles on Delta - I nearly always go East not West from LHR. So, I'm unfamiliar with US routes internally or from there East.
So far, I think the best route is LHR - Vancouer RTN, via Seattle. So a Delta hop from Seattle rtn Vancouver. (Delta or VS re LHR/Seattle rtn ? - miles are different, but are taxes?). I've no idea what the taxes are for the Seattle/Vancouver Delta rtn hop. This takes him back to London. I reckon this costs about £350 (290 tax for LHR/Seattle, the rest a guess for Delta Seattle/Vancouver)
Then LHR - Sing rtn on Sing airways - don't know the taxes for this. But I reckon it will be about £ 400.
So £750 total which is not too bad.
But it seems a long winded way to do it. If anyone has a better idea, I'd love to hear it. Please ignore if you have better things to do.
Thanks very much