Yes, both of them, enough unwanted dogs in the world without adding to them  
Also health benefits are good too (less cancer risks, no pyometra etc).

There are some low cost neutering clinics out there, we have one near us, in West Yorkshire, called Petvax - and they do neutering and vaccinations a lot cheaper than other places.  Neutering there is £40 (male) and £60 (female).  Puppy vaccines are £20, £15 for the booster.  Our Sky wont go on a bus though - so we had her done at our local vets.
Have you asked around the vets to see if they know of any near you?  Also, some vets will let you pay in instalments - that way you could spread the cost.

Just had a look and the Mayhew apparently do low cost neutering for low income owners.  RSPCA also do low cost neutering apparently.  

Here's some more info I borrowed from Cat Chat....



http://www.catchat.org/neuter.html#lowcost

I know it says it's a cat website, but these clinics say they're for both cats and dogs.

Hope this helps a bit

Oooh now that's a toughie.  Personally if I had a pup I'd choose to do it before their first season (if female) - so roughly 6 months-ish.  But there are some vets who say a female should have a season first.  Some people (not sure about vets, but breeders) say even longer, to make sure their...girl's bits are matured enough.
With males, the sooner the better for me, roughly 5-6 month mark I think, again, depending on the vet.  That way you shouldn't get that randy teenager dog who likes to jump the fence and beat other lads up  
It also depends also on whether this is going to be a show pet or not, as some say early neutering can give them a different shape (not as masculine, smaller frame).
But if it is just going to be a pet, go on what the vet suggests - they know what's best
In other words, I don't know!  I'm sure there are many here who will be able to give you more info.  
My two came to me as adults and we had them both neutered as adults.  Sky is somewhere between 4 and 6, and Badger is apparently around the 2-3 mark, although we think he's probably younger.

Edited to add - depending on when you get a bitch speyed, the risks of cancer differ a bit.  Before first season they're lowest, after a season it rises a bit, then after several the risks are a bit higher.  Pyometra is something else worth reading about, it's a nasty womb infection that can kill, the only cure for which would be an emergency spey anyway.  Of course, if a bitch is speyed early, then there is little risk of this (there is a form of pyometra in speyed females in the bit left behind - but this is very very rare).

Both of mine are neutered,Ellie was done 3 months after her first season on the advice of our vets and Rio was done at 7 months BUT I am a little concerned that for Rio may have done more harm than good,some people are suggesting that the introduction of testosterone brings with it more confidence and I will always  wonder if he would have been less nervous if we had let him develop a bit longer before lopping them off.

Still what's done is done I guess I'll never know

He looks like a sturdy little chap Mittenz !!

Molly, the Springer was already spayed when I got her a 7 months. Presuming she hadnt had a season, and reading comments on different forums, I find her coat is thick and wavy, and she now had incontinence, sucessfully being treated with Ephadrin.  This may be down to spaying so young. I had the other dogs spayed 3 months after their first season, and the boys at 6/7 months, or depending what age I had them, as soon as they arrived home! The vet said she could neuter Ted as soon as his testicles dropped, which was fortunated, as he was jumping anything, with or without pulse!

Yes Barb that was the reason my vet gave for waiting until after the first season.
How old was Molly when she became incontinent ?