Cheap ideas....hmm....the bubble bath thing, I've been known to do on occassion. But since you mentioned spring and the winter having had a bad affect on you, I'm thinking that perhaps you need to get out of the house. I get that way in the winter too where I feel trapped and want to get out.
Taking walks, exploring the parks, woods, etc. Go to the park, eat lunch and read a book. I'm not so good with gardening and sometimes that just seems like to much work - lol - but I'm an odd duck because I really enjoy mowing the lawn (love the smell the scent of freshly mowed grass). Shopping can also be another cheap thing to do (If you stick to the clearance areas and whatnot) and I tend to want to shop for new clothes and things that are season related. It gets me out of the house and helps with that new season/new beginning feeling that spring usually brings out in me.
I'm not sure what it all available in your area, but I'm sure you can find things to do. I found a few years ago, a book that had things going on in my area that I had never even known about and I've lived here all of my life (other than a year). That got me to really looking and being creative!
Hope you can find something to do to get you out of your rut. I know how depressing it feels to feel "stuck".