You all have helped with our upcoming April/May- 3 week tour of the UK and we are excited. Our last

You all have helped with our upcoming April/May- 3 week tour of the UK and we are excited. Our last full day will be spent in Windsor. Then we drop the rental car off at the airport in the early evening. my travel group We'll need to get to a hotel from the car rental drop-off site. Our next morning flight back to the USA leaves approx. 8 a.m. So, please advise what hotel we should book for that last night. We'll need to be at Terminal 4 by 5 a.m.
Departing from T4 in the morning I'd probably just stay at the Hilton, which is connected to T4 by a covered walk (use a luggage my travel group cart, which are always around.) Otherwise my travel group you'll have to use a taxi (if one will pick you up for a short run) or the Hotel Hoppa Bus ( 4 per person my travel group each way) which can be a giant pain in the early morning.
Have you checked what time the car hire place opens in the morning - some open as early as 5:00am. If so you could stay in Windsor that evening and have a civilised last meal before dropping the car off the next morning
Any of these are viable options. If the Hilton doesn't fit in the budget, then I'd probably PL and take a cab. The hoppa has gone up in price so a cab won't cost much more and you wouldn't have to ride around from hotel to hotel on the route.