A surf wetsuit isn't as comfortable for swimming in. The shoulders on a tri suit are designed for mobility in your stroke. They also have a different combo of weights of neoprene, and a different coating to make the suit move through water with less drag. It also depends on the body glove suit - but there are often restrictions in a triathlon as to what thicknesses of neoprene are allowed where (arms, legs, etc). Something you might want to check out about your suit and your races.

Will it work? Yeah, if you don't mind the restrictions on your stroke. But there are definitely cheaper tri suits available out there -- $450 is by no means required.

yeah, my local tri shop does entry tri wetsuits full-sleeve for 250ish

I will be doing my first tri's this summer and wanted a wetsuit. So I searched on ebay and found brand new one for $119. Orca S1 wetsuit...it's a entry level suit, but it should do the trick for myself not sure what you need? I think the sellers name was, wetsuitman?