Hi SUMMERFRUIT - yes my boars are exceptionally spoiled but they are Rescue boars so they reckon they deserve it. 
Biggest expense is their accomodation (hopefully a one off expense).
Mine have the DC old wooden playhouse (it just needed some minor indoor alterations)
Then a run (get a large rabbit run for security)
Indoor accomodation for winter nights.
Hay- I buy two bags for 10 days (4kg from The Range IIRC £3.99 a bag)
Veg- you'll have alot of it anyway with normal shopping.
I buy parsley, sweetcorn and salad bags as extra for the boys.
Pellets, about £10 for a large bag, I give a handful every day.
Bowls- large heavy ones that they can't tip up (I use dog bowls) and water bottles (that they don't drink from)
Storage for their hay, newspapers or whatever you are using.
I did look at Pet Insurance but it was expensive . If you save the money in a Guinea-Pigs Savings Account then you'll have it there.
Look out a Guinea-Pig savvy vet (hopefully you won't need them) or if you are near enough, the Cambridge Cavy Trust. (£35 per year regardless of how many pigs you have).
Get yourself a Guinea-Pig First Aid Box too. There's a thread on here from last year, but we can do a new one I'm sure.
They are lovely. Our boars belong to the DC , but DS is a bit meh so the little boy is mine .
We check them morning, they have an evening cuddle.
A couple of hours in their run (building up time now) .
Timewise: they have a fresh haybed (cardboard, newspaper, deep hay) every 2-3 days depending on how manky they are. Then the whole Pighouse emptied and cleaned weekly (they spend most of the time in the Haybox) When they were inside we did the cage every night, .
I'm sure I have particularly messy pigs though. They always try to outdo each other 
But hey are rewarding- the wheeking and purring
The smug look of GP1 when my DD puts him on her shoulder.
The purring of GP2 when we have a look in the fridge.