Last October I bought my first GPS receiver - the Magellan 315. At the store there were umpteen different units to buy. But I started cheap for a number of reasons.
First, I was not sure what all the different things on a GPS did. Yeah, I know what mapping did, but not some of the other things. Even though the 315 is one of the simplest things in the world to use, it still took me a month or so to finally get well aquainted with it. I found that most of the stuff that was being shown to me I was just not using.
I normally only have a few of the screens turned on for use - the compass, map, sat status, and maybe one of the To: screens.
Next is price: A few weeks ago I bought a Street Pilot III for use as a cool geek toy in the car. It cost 4 times as much as my 315 and provides 1/8th the information that the 315 spits out. But, it is meant to do street routing - and it does it pretty well. It is nowhere near exact when it comes to "fastest route" or "shortest route", but it does work.
Last weekend I bought a Magellan Meridian - the base model. It has all the features of the 315, plus has that nifty card slot. Yes, it only has a 2 MB base map, but I will get to that in a moment. It also has a few more bells and whistles than the 315, but what more I can't really be sure of right now. I do like the thing a lot, but I am still learning it and finding what is useful and what is not. The useless functions will be turned off soon.
Now - as for the base map... I honestly don't care about that. I can slap a 128 meg card in there and take care of any mapping that I need done. All I have right now is a 16 meg card and I am only using 7 meg for that, and that covers almost 1/3 of the state, and a much larger area than I am ever going to be able to cover in geocaching over a month long period.
So, I guess my point is this - get something good that is going to get you started. Don't think that you need to have all the latest bells and whistles. Yeah, they are cool in that geek factor way, but when it comes down to it you will probably find that most of the stuff is just nice frills - for instance the temperature gauge. I saw a comedian back about 10 years ago who was complaining about the weather people on tv. His comment was something along the lines of "I can't tell the difference between 61 and 63. Just tell me if I need a coat!" (Jerry Seinfeld maybe?) The same is kind of true, to me, of the base map. If you are going to be in an area, you are probably going to have the detail map loaded up. In that case, the size of the base map matters not one bit.
Anyway, hope this helps some.