I'd say a guinea pig is a good pet but they aren't as easy as they sound, i recently helped an elderly gentleman get everything together to adopt some, as people have previously said as a pro rescue forum, we recommend adopting instead of pet shop pigs, the gentleman i know that adopted them became alot less lonely because guinea pigs are just such great little characters !
So lets start with a list of what you need !
A Cage, Guinea pigs also need alot of space, a cage must be the minimum of a 120 cage for 2 guinea pigs, and obviously guinea pigs are social creatures so boys should be kept in pairs (groups bigger with boys rarely work) and girls can be kept in anything more that 2 ! This website should help you, it recommends a C&C cage, it will explain it on the website there lovely and alot more versatile than a shop bought cage.
http://www.guineapigcages.com/
A Run, Referring back to needing alot of space, guinea pigs need alot of exercise ! And as exercise balls and wheels are out of the question due to there delicate backs, you need a run, a run should be bigger than the piggies actual living space so there cage basically, this run can be for indoor and outdoor or you can have one for each !
Food, the most important thing to a piggy ! Nuggets are the base of a piggies diet, there is alot of mixed feed's that we don't recommend due to promoting selective feeding but if you want to know more about that you can search it, we promote nuggets that usually look like guinea pig poo basically, there are several brands that people use and personally i use Burgess (: On top of nuggets, they need hay available at all times, this should be in a hay rack and also can be used in the cage for extra warm bedding ! Hay is for keeping the teeth in good order too ! Also piggies need daily fresh veggies, theres a list of veggies you can feed them here
http://www.theguineapigforum.co.uk/showthread.php?t=42
Of course this requires a water bottle (not a bowl) a veg bowl and a nugget bowl, some people recommend if you have boars that you buy two of everything so they have there own things.
Bedding, there is so much bedding to choose from, Sawdust is great but often the dust in it can be dangerous for there breathing, and sometimes it can get in the piggies eye causing damage, i've experienced both of these things. Carefresh is a safer paper based bedding which alot of people love, although expensive cheaper brands can be bought, Vet bed, this is a bedding that requires alot more work, and need's to be changed and washed and poop scooped regularly, along with fleece as a bedding, fleece requires daily poop scooping and washing around every 3 days but looks great and piggies find it super comfey !
Vet Bills, guinea pigs do need fairly regular nail clipping and untill you feel safe yourself doing this you may want it done by a vet costing between £4-£10 a time, on the other hand if you adopt the rescue may provide this service free of charge ! As i mentioned in bedding piggies do sometimes just end up hurting themselves with different things and this can total up a bit, a check up for my piggies to just see a vet before any medication is about £18 ! then obviously you need to buy anything he prescribes after that, Luckily i haven't had to make to many trips to the vets so far in my piggy owning life !
Toys, Piggies need something to keep them active, tunnels, willow balls, and natural treats are great, as well as the essential hidey places like igloos ! But not all toys need to be bought, piggies can find fun in simple things like paper bags and toilet rolls, once you start searching you can find some really great and cheap ideas !
Time, Piggies require alot of time ! they like to be loved and played with, they require there run around time for about an hour and more if you can daily, the also need you to take the time to chop up there veggies every day (i do mine at night but you can do it whenever really) so if you don't have the time to do all these things including the piggie shopping they may not be for you !
Obviously the starting up cost is alot more then day to day costs ! a cage can be normally £50 for a good size one, and then you need the odd little bits like hairbrushes and things, if you go into your local pet shop they can help you price things up (:
They may recommend things like water drops for vitamins and these just aren't necessary and can sometimes put piggies off there water,
Another cost is if you become an addict like me and many others i started of with just 2 and within 4 months i had 5 and i still want more haha!
I can't really say guinea pigs are easier than rabbits as i don't know anything about rabbits !
Good luck with your pottential piggie future !