Yes, you just turn up at the immigration desk in Philippines and receive a stamp for 21 days visa free. If you want more it's no problem but just say so here.
You MUST be in possession of either a return air ticket or an onward ticket. In fact these days you'd be lucky if the airline would allow you to fly into Philippines without that. Don't be fooled by anyone who tells you differently!!
Well, I admire your sense of adventure and of course it's a personal choice. Many folks do drive there without problems, but imho many more have had problems. My own personal view is that I would rather pay someone else to drive and I'll just chill out.
For me, not knowing where I'm going to is an issue. Not having roadsigns/directions is an issue. Not feeling able to predict the behaviour of other road users is an issue. The biggest problem imho is that as a foreigner, in any kind of issue on the road YOU are going to be wrong, even if your right and it may build up into a bigger challenge.
Do a search here in the forum to reveal what others think. I'm not trying to change your mind just giving my reasons why I think it may not be the best plan for everyone to step off that plane into the Philippines for the first time and get behind the driving wheel.
You UK licence is OK for 90 days. Sorry I can't help you with prices, but do be sure you are very well covered with a good and reputable fully comprehensive insurance cover!!
Don't be hesitant to move to another one if your not totally comfortable with the hotel facilities or with the locality.
You'll need to consider that carefully. Do not be tempted to take oodles of wonga in cash with you. Especially as you not that sure of where you are staying.
Looks like you'll need to rely on a combination of cash/Debit cards/Credit cards etc. I wouldn't bother with travellers Cheques.
You'll find that the local money changers offer pretty good rates. But do be sure to use only reputable ones.
Please don't roam around with significant cash in your pocket!!!
Here's something that works well for me.
I've been using the Caxton pre-paid card for quite some time now and have found it to suit me exactly. I have 3 cards. A dollar card, a Euro card and a Global Traveller Card in £'s
The dollar and Euro cards get loaded at the exchange rates on the day you load them, not on the day you 'spend' them, so you have a nice chance to play the markets. Always worked for me so far this year.
The other benefit is that the card(s) can be loaded up with cash at any time from your UK bank account online, by telephone or by text.That way your risk is contained somewhat.
BTW, you can get extra cards in the name of your nearest and dearest that also can be loaded from your UK bank in the same way.
Alternatively consider sending remittances to your Philippine bank (if you have one)
That's the way I work it anyway. I'm sure other folks have their favorite ways too.
Always consider security and minimising the risks. There's really not much you can do to control exchange rates, which actually won't change hugely during a month anyway.
Just my 2 centavos