A 60 gallon tank can make a nice beginner size, so long as you are aware of the limits of your system. 60 gallons is small by marine standards, so realize that most fish which you see at the LFS are not going to be options for you. You will need to restrict yourself to fish with an adult size of 6'' or less, and at the same time take behavior into consideration.
As for equipment, the tank does not have to be overly expensive, but there are common traits for all marine systems that you will need to be successful. Your filtration system will consist of a protein skimmer, live rock, and aragonite sand. For more information on this filtration method, as compared to what you have used previously on freshwater systems, check out this link: http://www.tropicalfishkeeping.com/m...shwater-31955/
For a 60 gallon tank, assuming you go fish-only for your first attempt at saltwater, here are some basic options. For a protein skimmer to cut back on costs, I would consider a hang on skimmer. The AquaC Remora is the best option for this purpose. It will cost you about $250 mail order, including skimmer and prefilter box: AquaC Remora Pro Protein Skimmer with Rio 1400 Pump AquaC Surface Prefilter Box
Trust me, $250 is NOT a lot of money. The skimmer is BY FAR the more important piece of equipment you will have on your tank. If you are not willing to spend $250 on a skimmer, then just forget about saltwater. If you read the article above on marine filtration systems, then you understand how important it is to have a high quality protein skimmer.
Moving on to live rock. This is an area where a lot of people become intimidated because the price of the live rock at the LFS is extremely high. You only need to "seed" the tank with actual live rock. The rest can be dry rock. I purchase my dry rock from Marco Rocks The finest aquarium rock available, base rock, live rock, reef rock, marco rock, reef tank saltwater fish, live corals, Marco rocks, Fiji live rock, Tonga Live rock
. You can order 40 pounds of dry rock and 40 pounds of aragonite sand for $109. You will need 2 times this amount for a 60 gallon tank, meaning 80 pounds of dry rock and 80 pounds of sand. This rock will quickly become "live" when you place it into your aquarium, seeded with about 10 pounds of live rock from the LFS. Lets assume $80 on live rock + $218 dry rock & sand = $289 total on rock and sand.
So, you have about $540 to spend on the guts of your system. This isn't much money at all for a marine conversion and you will have a VERY good setup that is capable of providing an outstanding life support system to your marine livestock. You will obviously have some small add ons, such as salt mix, test kits, etc. But the actual filtration system will be complete.
Also, you may have a few pieces of freshwater equipment that we can use. The filtration system will be 100% USELESS, but we may be able to use some power heads or hang on filters simply for the purpose of water movement, which is extremely important in a marine system. Your heater may also be adequate. Also, the lighting can be used for now, until such times as you decide to add corals to the tank.