I don't think it's recommended to switch out rigid forks for suspension forks (changes frame geometry). If you wanted to swap out parts with a new frame and fork, then the bottom bracket, front derailleur, seatpost, seatpost clamp and headset/forks would need to fit.

According to what I've read, the Suntour fork hierarchy is XCT < XCM < XCR (and Raidon etc.). For Rockshox, XC28 < XC30 < XC32 then Recon Silver and others. The ones below the Suntour XCR and Rockshox XC30 I read were not recommended. The Suntour XCR and Rockshox XC30 may be somewhat comparable but I read a message from someone saying he broke 2 Suntour XCR forks in 13 months. There are some pretty cheap Suntour XCR on eBay so it's very tempting. There are lots of replacements parts for Rockshox XC30 and this is one of the reasons I bought a Rockshox XC30 on acycles.fr

If you wanted a high quality build you could go with this fork (Marzocchi Marathon 26") MARZOCCHI MARATHON LR Fork 26" 100 mm AER LR Tapered Red - Probikeshop
with this frame Viper X-team VIPER X-TEAM 26" MTB Frame White/Red 2014 - Probikeshop Both take 26 inch wheels and tapered forks.

Or, a cheaper alternative would be this fork, Rockshox Recon Silver RockShox Recon Silver TK 26" 100mm QR Suspension Fork and this frame, Access XCL Access XCL Comp 26" Mountain Bike Frame

Or, an even cheaper alternative than that would be this frame Nashbar aluminium mountain Nashbar 26" Mountain Bike Frame and this fork, Rockshox XC30 Rock Shox Xc30 TK Coil 26'' Federgabel Canti/disc 100mm 1 1/8'' 9QR schwarz Mod. 2014

The last two choices are with standard 1-1/8" straight steering tube and V-brake compatible. I prefer the simplicity of V-brakes anyway.

EDIT: I found another you could pair, this one would take 27.5 inch wheels. Dartmoor Hornet frame http://www.bike24.com/1.php?content=...gc=0;orderby=2 and S.R. Suntour Raidon fork http://www.bike24.com/1.php?content=...gc=0;orderby=2 Both are compatible with tapered fork and 120mm travel.

ANOTHER EDIT: Wow, I just found a Manitou Minute Pro fork for $250 http://www.pricepoint.com/Brand/Mani...140mm-Fork.axd It's 100mm travel with a tapered steering tube. That one I'd put in first place then the Rockshox Recon Silver in second.