You don't need a mapping GPS for Audaxing.
I do all my Audaxing with a £70 Garmin eTrex and use routes built up of routepoints (one per routesheet instruction) with names encoding the routesheet instruction (L, R, SO, etc). There's also no software to buy (I use free stuff) or maps to purchase.
This was my route for the Willy Warmer 200:
Bicycle Path - Willy Warmer 2009 at Bikely.comIt needed splitting into two separate routes (as there's a limit of 120 points per route on the Garmin eTrex) and there are some other quirks but you get used to them.
I'll be using my old eTrex for LEL. No mapping.
If I was to start again though I'd probably go for a Legend HCx (the old bog standard eTrex doesn't use USB and the non-standard cable costs £20) and download/install the OpenStreetMap stuff (see GPS sub-forum) for free.