you'll find a million answers to your questions, but after having owned both SN and RN and modded them both. I would go back to a SN without any reservation. Alot of peeps will bang on the SN's, but you can get a ton of ski in a SN setup for you money. There are no real advantages to having the RN except aesthetics and if you'll search you can find the thread where we listed "sweet squares." There were some well built machines. That being said, I had RN envy when I ran my squares and then bought one. Now having been on both sides I'd go back and not miss my RN. I picked up a SN in real good condition for 1500 and it had some mods (pipe, prop, footholds, intake) whereas I bought a RN that was bone stock and still payed 2k for it. As long as the engine's a 701 and in decent shape the sky is the limit for your mods and being on a budget you def. can get plenty of good mods for your ski with the remaining 1000+ dollars you'll have if you bought a SN. Some basic mods...
Foot Holds - $75
Turf/padding - $100
High Compression/girdled head - $250
Bpipe - $300-500
Swirl prop - $100-200
MSD enhancer or total loss ign - $150-400
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$925 - 1525...depending on how picky you are as a shopper.
I've been able to find plenty of good deals from members on here and pwc today. I learned a ton by doing those builds and asking questions on here, but every minute you spend wrenching is a minute you could be riding. For your $2500 budget I think if you'll be patient you'll be able to find a nice ski with some mods already done for you.
Don't be afraid to hunt CL (via Search Tempest). Most of the guys on here will post good deals from CL throughout the country.